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 $110.51   13.677%   $125.6245   $125.62   $125.60   $125.60  
  Purchase #2 $239.72   5.702%   $253.3888   $253.39   $253.40   $253.40  
  Purchase #3 $25.60   6.360%   $27.2282   $27.23   $27.25   $27.20  
  Purchase #4 $148.75   12.805%   $167.7974   $167.80   $167.80   $167.80  
  Purchase #5 $224.28   8.688%   $243.7654   $243.77   $243.75   $243.80  
  Purchase #6 $135.97   12.206%   $152.5665   $152.57   $152.55   $152.60  
  Purchase #7 $40.64   8.731%   $44.1883   $44.19   $44.20   $44.20  
  7 purchase totals = $925.47       $1,014.5591   $1,014.57   $1,014.55   $1,014.60