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 $111.99   12.580%   $126.0783   $126.08   $126.10   $126.10  
  Purchase #2 $216.83   11.178%   $241.0673   $241.07   $241.05   $241.10  
  Purchase #3 $33.54   3.161%   $34.6002   $34.60   $34.60   $34.60  
  Purchase #4 $241.82   9.165%   $263.9828   $263.98   $264.00   $264.00  
  Purchase #5 $233.82   11.232%   $260.0827   $260.08   $260.10   $260.10  
  Purchase #6 $215.87   7.442%   $231.935   $231.94   $231.95   $231.90  
  Purchase #7 $160.50   3.479%   $166.0838   $166.08   $166.10   $166.10  
  7 purchase totals = $1,214.37       $1,323.8301   $1,323.83   $1,323.90   $1,323.90