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 $222.96   10.578%   $246.5447   $246.54   $246.55   $246.50  
  Purchase #2 $178.60   3.506%   $184.8617   $184.86   $184.85   $184.90  
  Purchase #3 $63.26   4.470%   $66.0877   $66.09   $66.10   $66.10  
  Purchase #4 $168.44   11.201%   $187.307   $187.31   $187.30   $187.30  
  Purchase #5 $62.56   11.864%   $69.9821   $69.98   $70.00   $70.00  
  Purchase #6 $187.70   9.500%   $205.5315   $205.53   $205.55   $205.50  
  Purchase #7 $236.75   10.183%   $260.8583   $260.86   $260.85   $260.90  
  7 purchase totals = $1,120.27       $1,221.1730   $1,221.17   $1,221.20   $1,221.20