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 $17.82   7.657%   $19.1845   $19.18   $19.20   $19.20  
  Purchase #2 $231.40   3.398%   $239.263   $239.26   $239.25   $239.30  
  Purchase #3 $41.30   5.266%   $43.4749   $43.47   $43.45   $43.50  
  Purchase #4 $67.65   5.401%   $71.3038   $71.30   $71.30   $71.30  
  Purchase #5 $206.96   6.412%   $220.2303   $220.23   $220.25   $220.20  
  Purchase #6 $95.86   6.198%   $101.8014   $101.80   $101.80   $101.80  
  Purchase #7 $203.71   4.127%   $212.1171   $212.12   $212.10   $212.10  
  7 purchase totals = $864.70       $907.3750   $907.36   $907.35   $907.40