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 $84.83   7.616%   $91.2907   $91.29   $91.30   $91.30  
  Purchase #2 $149.49   7.463%   $160.6464   $160.65   $160.65   $160.60  
  Purchase #3 $215.96   5.392%   $227.6046   $227.60   $227.60   $227.60  
  Purchase #4 $250.95   9.734%   $275.3775   $275.38   $275.40   $275.40  
  Purchase #5 $59.45   4.355%   $62.039   $62.04   $62.05   $62.00  
  Purchase #6 $217.99   3.704%   $226.0643   $226.06   $226.05   $226.10  
  Purchase #7 $35.43   8.258%   $38.3558   $38.36   $38.35   $38.40  
  7 purchase totals = $1,014.10       $1,081.3783   $1,081.38   $1,081.40   $1,081.40