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 $162.27   5.479%   $171.1608   $171.16   $171.15   $171.20  
  Purchase #2 $23.50   13.328%   $26.6321   $26.63   $26.65   $26.60  
  Purchase #3 $48.76   12.427%   $54.8194   $54.82   $54.80   $54.80  
  Purchase #4 $239.84   5.730%   $253.5828   $253.58   $253.60   $253.60  
  Purchase #5 $201.91   3.620%   $209.2191   $209.22   $209.20   $209.20  
  Purchase #6 $213.87   8.464%   $231.972   $231.97   $231.95   $232.00  
  Purchase #7 $42.57   5.222%   $44.793   $44.79   $44.80   $44.80  
  7 purchase totals = $932.72       $992.1792   $992.17   $992.15   $992.20