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 $91.57   7.718%   $98.6374   $98.64   $98.65   $98.60  
  Purchase #2 $124.34   9.743%   $136.4544   $136.45   $136.45   $136.50  
  Purchase #3 $60.40   9.287%   $66.0093   $66.01   $66.00   $66.00  
  Purchase #4 $166.51   11.362%   $185.4289   $185.43   $185.45   $185.40  
  Purchase #5 $68.61   11.582%   $76.5564   $76.56   $76.55   $76.60  
  Purchase #6 $204.38   9.623%   $224.0475   $224.05   $224.05   $224.00  
  Purchase #7 $9.98   12.716%   $11.2491   $11.25   $11.25   $11.20  
  7 purchase totals = $725.79       $798.3830   $798.39   $798.40   $798.30