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 $62.65   6.573%   $66.768   $66.77   $66.75   $66.80  
  Purchase #2 $118.68   8.766%   $129.0835   $129.08   $129.10   $129.10  
  Purchase #3 $156.91   8.646%   $170.4764   $170.48   $170.50   $170.50  
  Purchase #4 $60.30   9.668%   $66.1298   $66.13   $66.15   $66.10  
  Purchase #5 $23.36   6.827%   $24.9548   $24.95   $24.95   $25.00  
  Purchase #6 $130.76   12.843%   $147.5535   $147.55   $147.55   $147.60  
  Purchase #7 $200.78   5.155%   $211.1302   $211.13   $211.15   $211.10  
  7 purchase totals = $753.44       $816.0962   $816.09   $816.15   $816.20