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 $87.67   9.634%   $96.1161   $96.12   $96.10   $96.10  
  Purchase #2 $174.31   3.697%   $180.7542   $180.75   $180.75   $180.80  
  Purchase #3 $119.56   11.647%   $133.4852   $133.49   $133.50   $133.50  
  Purchase #4 $164.61   10.208%   $181.4134   $181.41   $181.40   $181.40  
  Purchase #5 $232.75   10.504%   $257.1981   $257.20   $257.20   $257.20  
  Purchase #6 $183.52   6.622%   $195.6727   $195.67   $195.65   $195.70  
  Purchase #7 $102.94   9.576%   $112.7975   $112.80   $112.80   $112.80  
  7 purchase totals = $1,065.36       $1,157.4372   $1,157.44   $1,157.40   $1,157.50