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 $56.77   9.850%   $62.3618   $62.36   $62.35   $62.40  
  Purchase #2 $131.40   8.513%   $142.5861   $142.59   $142.60   $142.60  
  Purchase #3 $86.46   6.850%   $92.3825   $92.38   $92.40   $92.40  
  Purchase #4 $240.60   5.273%   $253.2868   $253.29   $253.30   $253.30  
  Purchase #5 $60.84   11.728%   $67.9753   $67.98   $68.00   $68.00  
  Purchase #6 $177.58   11.355%   $197.7442   $197.74   $197.75   $197.70  
  Purchase #7 $150.69   4.700%   $157.7724   $157.77   $157.75   $157.80  
  7 purchase totals = $904.34       $974.1091   $974.11   $974.15   $974.20