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 $39.62   4.421%   $41.3716   $41.37   $41.35   $41.40  
  Purchase #2 $206.66   3.415%   $213.7174   $213.72   $213.70   $213.70  
  Purchase #3 $96.31   8.600%   $104.5927   $104.59   $104.60   $104.60  
  Purchase #4 $187.45   7.738%   $201.9549   $201.95   $201.95   $202.00  
  Purchase #5 $97.86   3.852%   $101.6296   $101.63   $101.65   $101.60  
  Purchase #6 $70.74   4.525%   $73.941   $73.94   $73.95   $73.90  
  Purchase #7 $23.52   9.183%   $25.6798   $25.68   $25.70   $25.70  
  7 purchase totals = $722.16       $762.8870   $762.88   $762.90   $762.90