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 $40.69   5.819%   $43.0578   $43.06   $43.05   $43.10  
  Purchase #2 $231.26   12.710%   $260.6531   $260.65   $260.65   $260.70  
  Purchase #3 $52.33   12.804%   $59.0303   $59.03   $59.05   $59.00  
  Purchase #4 $6.36   11.269%   $7.0767   $7.08   $7.10   $7.10  
  Purchase #5 $22.96   10.148%   $25.29   $25.29   $25.30   $25.30  
  Purchase #6 $87.84   6.642%   $93.6743   $93.67   $93.65   $93.70  
  Purchase #7 $186.79   10.501%   $206.4048   $206.40   $206.40   $206.40  
  7 purchase totals = $628.23       $695.1870   $695.18   $695.20   $695.30