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 $197.27   8.357%   $213.7559   $213.76   $213.75   $213.80  
  Purchase #2 $228.42   3.297%   $235.951   $235.95   $235.95   $236.00  
  Purchase #3 $153.76   13.596%   $174.6652   $174.67   $174.65   $174.70  
  Purchase #4 $231.85   8.375%   $251.2674   $251.27   $251.25   $251.30  
  Purchase #5 $50.64   10.746%   $56.0818   $56.08   $56.10   $56.10  
  Purchase #6 $167.37   11.777%   $187.0812   $187.08   $187.10   $187.10  
  Purchase #7 $230.91   13.688%   $262.517   $262.52   $262.50   $262.50  
  7 purchase totals = $1,260.22       $1,381.3195   $1,381.33   $1,381.30   $1,381.50