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 $93.67   5.331%   $98.6635   $98.66   $98.65   $98.70  
  Purchase #2 $245.73   9.315%   $268.6197   $268.62   $268.60   $268.60  
  Purchase #3 $179.56   6.739%   $191.6605   $191.66   $191.65   $191.70  
  Purchase #4 $191.99   5.661%   $202.8586   $202.86   $202.85   $202.90  
  Purchase #5 $166.88   5.517%   $176.0868   $176.09   $176.10   $176.10  
  Purchase #6 $29.82   11.313%   $33.1935   $33.19   $33.20   $33.20  
  Purchase #7 $138.33   10.638%   $153.0455   $153.05   $153.05   $153.00  
  7 purchase totals = $1,045.98       $1,124.1281   $1,124.13   $1,124.10   $1,124.20