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 $193.36   13.392%   $219.2548   $219.25   $219.25   $219.30  
  Purchase #2 $125.71   9.512%   $137.6675   $137.67   $137.65   $137.70  
  Purchase #3 $243.48   3.313%   $251.5465   $251.55   $251.55   $251.50  
  Purchase #4 $25.38   7.445%   $27.2695   $27.27   $27.25   $27.30  
  Purchase #5 $224.88   11.651%   $251.0808   $251.08   $251.10   $251.10  
  Purchase #6 $232.52   4.565%   $243.1345   $243.13   $243.15   $243.10  
  Purchase #7 $159.34   7.314%   $170.9941   $170.99   $171.00   $171.00  
  7 purchase totals = $1,204.67       $1,300.9477   $1,300.94   $1,300.95   $1,301.00