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 $151.49   8.242%   $163.9758   $163.98   $164.00   $164.00  
  Purchase #2 $234.70   8.734%   $255.1987   $255.20   $255.20   $255.20  
  Purchase #3 $152.47   8.837%   $165.9438   $165.94   $165.95   $165.90  
  Purchase #4 $82.57   6.717%   $88.1162   $88.12   $88.10   $88.10  
  Purchase #5 $247.50   8.112%   $267.5772   $267.58   $267.60   $267.60  
  Purchase #6 $47.66   3.828%   $49.4844   $49.48   $49.50   $49.50  
  Purchase #7 $26.35   5.654%   $27.8398   $27.84   $27.85   $27.80  
  7 purchase totals = $942.74       $1,018.1359   $1,018.14   $1,018.20   $1,018.10