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 $204.49   13.162%   $231.405   $231.41   $231.40   $231.40  
  Purchase #2 $59.53   4.248%   $62.0588   $62.06   $62.05   $62.10  
  Purchase #3 $157.29   11.114%   $174.7712   $174.77   $174.75   $174.80  
  Purchase #4 $213.75   4.497%   $223.3623   $223.36   $223.35   $223.40  
  Purchase #5 $171.51   8.651%   $186.3473   $186.35   $186.35   $186.30  
  Purchase #6 $78.75   6.432%   $83.8152   $83.82   $83.80   $83.80  
  Purchase #7 $155.56   9.849%   $170.8811   $170.88   $170.90   $170.90  
  7 purchase totals = $1,040.88       $1,132.6409   $1,132.65   $1,132.60   $1,132.70