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 $86.91   11.445%   $96.8568   $96.86   $96.85   $96.90  
  Purchase #2 $109.71   8.394%   $118.9191   $118.92   $118.90   $118.90  
  Purchase #3 $96.51   7.430%   $103.6807   $103.68   $103.70   $103.70  
  Purchase #4 $36.92   5.254%   $38.8598   $38.86   $38.85   $38.90  
  Purchase #5 $215.52   7.384%   $231.434   $231.43   $231.45   $231.40  
  Purchase #6 $245.31   3.771%   $254.5606   $254.56   $254.55   $254.60  
  Purchase #7 $159.32   6.518%   $169.7045   $169.70   $169.70   $169.70  
  7 purchase totals = $950.20       $1,014.0155   $1,014.01   $1,014.00   $1,014.10