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 $59.52   9.622%   $65.247   $65.25   $65.25   $65.20  
  Purchase #2 $156.45   8.294%   $169.426   $169.43   $169.45   $169.40  
  Purchase #3 $159.55   4.438%   $166.6308   $166.63   $166.65   $166.60  
  Purchase #4 $197.73   9.138%   $215.7986   $215.80   $215.80   $215.80  
  Purchase #5 $110.72   10.634%   $122.494   $122.49   $122.50   $122.50  
  Purchase #6 $38.72   7.378%   $41.5768   $41.58   $41.60   $41.60  
  Purchase #7 $161.67   4.783%   $169.4027   $169.40   $169.40   $169.40  
  7 purchase totals = $884.36       $950.5759   $950.58   $950.65   $950.50