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 $46.50   13.592%   $52.8203   $52.82   $52.80   $52.80  
  Purchase #2 $185.48   6.510%   $197.5547   $197.55   $197.55   $197.60  
  Purchase #3 $64.35   10.453%   $71.0765   $71.08   $71.10   $71.10  
  Purchase #4 $95.86   12.855%   $108.1828   $108.18   $108.20   $108.20  
  Purchase #5 $209.94   12.562%   $236.3127   $236.31   $236.30   $236.30  
  Purchase #6 $54.84   8.739%   $59.6325   $59.63   $59.65   $59.60  
  Purchase #7 $122.48   10.694%   $135.578   $135.58   $135.60   $135.60  
  7 purchase totals = $779.45       $861.1575   $861.15   $861.20   $861.20