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 $158.87   9.243%   $173.5544   $173.55   $173.55   $173.60  
  Purchase #2 $36.82   8.445%   $39.9294   $39.93   $39.95   $39.90  
  Purchase #3 $182.53   11.762%   $203.9992   $204.00   $204.00   $204.00  
  Purchase #4 $249.93   8.650%   $271.5489   $271.55   $271.55   $271.50  
  Purchase #5 $203.40   9.559%   $222.843   $222.84   $222.85   $222.80  
  Purchase #6 $195.56   3.619%   $202.6373   $202.64   $202.65   $202.60  
  Purchase #7 $179.77   6.712%   $191.8362   $191.84   $191.85   $191.80  
  7 purchase totals = $1,206.88       $1,306.3484   $1,306.35   $1,306.40   $1,306.20