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 $202.86   11.753%   $226.7021   $226.70   $226.70   $226.70  
  Purchase #2 $123.92   12.601%   $139.5352   $139.54   $139.55   $139.50  
  Purchase #3 $41.86   9.172%   $45.6994   $45.70   $45.70   $45.70  
  Purchase #4 $44.40   3.255%   $45.8452   $45.85   $45.85   $45.80  
  Purchase #5 $10.53   8.311%   $11.4051   $11.41   $11.40   $11.40  
  Purchase #6 $59.62   8.239%   $64.5321   $64.53   $64.55   $64.50  
  Purchase #7 $236.68   13.151%   $267.8058   $267.81   $267.80   $267.80  
  7 purchase totals = $719.87       $801.5249   $801.54   $801.55   $801.40