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 $163.55   13.834%   $186.1755   $186.18   $186.20   $186.20  
  Purchase #2 $195.48   8.412%   $211.9238   $211.92   $211.90   $211.90  
  Purchase #3 $38.35   8.302%   $41.5338   $41.53   $41.55   $41.50  
  Purchase #4 $195.74   12.200%   $219.6203   $219.62   $219.60   $219.60  
  Purchase #5 $67.73   3.108%   $69.835   $69.84   $69.85   $69.80  
  Purchase #6 $169.74   12.215%   $190.4737   $190.47   $190.45   $190.50  
  Purchase #7 $51.52   12.721%   $58.0739   $58.07   $58.05   $58.10  
  7 purchase totals = $882.11       $977.6360   $977.63   $977.60   $977.60