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 $195.32   12.446%   $219.6295   $219.63   $219.65   $219.60  
  Purchase #2 $65.56   3.749%   $68.0178   $68.02   $68.00   $68.00  
  Purchase #3 $120.90   3.625%   $125.2826   $125.28   $125.30   $125.30  
  Purchase #4 $100.35   3.187%   $103.5482   $103.55   $103.55   $103.50  
  Purchase #5 $109.28   8.183%   $118.2224   $118.22   $118.20   $118.20  
  Purchase #6 $54.96   11.693%   $61.3865   $61.39   $61.40   $61.40  
  Purchase #7 $61.40   8.488%   $66.6116   $66.61   $66.60   $66.60  
  7 purchase totals = $707.77       $762.6986   $762.70   $762.70   $762.60