Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $156.75   8.631%   $170.2791   $170.28   $170.30   $170.30  
  Purchase #2 $241.76   9.464%   $264.6402   $264.64   $264.65   $264.60  
  Purchase #3 $234.90   6.563%   $250.3165   $250.32   $250.30   $250.30  
  Purchase #4 $107.69   11.797%   $120.3942   $120.39   $120.40   $120.40  
  Purchase #5 $116.32   9.625%   $127.5158   $127.52   $127.50   $127.50  
  Purchase #6 $217.99   5.782%   $230.5942   $230.59   $230.60   $230.60  
  Purchase #7 $197.61   4.750%   $206.9965   $207.00   $207.00   $207.00  
  7 purchase totals = $1,273.02       $1,370.7365   $1,370.74   $1,370.75   $1,370.70