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 $19.75   7.201%   $21.1722   $21.17   $21.15   $21.20  
  Purchase #2 $147.56   8.173%   $159.6201   $159.62   $159.60   $159.60  
  Purchase #3 $235.83   13.431%   $267.5043   $267.50   $267.50   $267.50  
  Purchase #4 $45.91   4.716%   $48.0751   $48.08   $48.10   $48.10  
  Purchase #5 $189.46   10.373%   $209.1127   $209.11   $209.10   $209.10  
  Purchase #6 $221.42   9.782%   $243.0793   $243.08   $243.10   $243.10  
  Purchase #7 $245.44   7.837%   $264.6751   $264.68   $264.70   $264.70  
  7 purchase totals = $1,105.37       $1,213.2388   $1,213.24   $1,213.25   $1,213.30