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 $91.48   7.390%   $98.2404   $98.24   $98.25   $98.20  
  Purchase #2 $62.65   6.381%   $66.6477   $66.65   $66.65   $66.60  
  Purchase #3 $165.88   13.673%   $188.5608   $188.56   $188.55   $188.60  
  Purchase #4 $245.46   9.400%   $268.5332   $268.53   $268.55   $268.50  
  Purchase #5 $85.63   10.786%   $94.8661   $94.87   $94.85   $94.90  
  Purchase #6 $115.96   12.179%   $130.0828   $130.08   $130.10   $130.10  
  Purchase #7 $173.85   8.300%   $188.2796   $188.28   $188.30   $188.30  
  7 purchase totals = $940.91       $1,035.2106   $1,035.21   $1,035.25   $1,035.20