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 $210.54   10.619%   $232.8972   $232.90   $232.90   $232.90  
  Purchase #2 $229.89   13.142%   $260.1021   $260.10   $260.10   $260.10  
  Purchase #3 $38.55   6.643%   $41.1109   $41.11   $41.10   $41.10  
  Purchase #4 $115.73   13.817%   $131.7204   $131.72   $131.70   $131.70  
  Purchase #5 $18.44   12.139%   $20.6784   $20.68   $20.70   $20.70  
  Purchase #6 $219.79   13.831%   $250.1892   $250.19   $250.20   $250.20  
  Purchase #7 $162.87   11.114%   $180.9714   $180.97   $180.95   $181.00  
  7 purchase totals = $995.81       $1,117.6696   $1,117.67   $1,117.65   $1,117.70