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 $195.54   3.313%   $202.0182   $202.02   $202.00   $202.00  
  Purchase #2 $41.85   9.194%   $45.6977   $45.70   $45.70   $45.70  
  Purchase #3 $66.56   13.801%   $75.7459   $75.75   $75.75   $75.70  
  Purchase #4 $26.25   6.369%   $27.9219   $27.92   $27.90   $27.90  
  Purchase #5 $11.88   11.131%   $13.2024   $13.20   $13.20   $13.20  
  Purchase #6 $147.63   9.173%   $161.1721   $161.17   $161.15   $161.20  
  Purchase #7 $137.55   3.355%   $142.1648   $142.16   $142.15   $142.20  
  7 purchase totals = $627.26       $667.9230   $667.92   $667.85   $667.90