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 $110.45   11.141%   $122.7552   $122.76   $122.75   $122.80  
  Purchase #2 $244.28   4.344%   $254.8915   $254.89   $254.90   $254.90  
  Purchase #3 $189.49   7.862%   $204.3877   $204.39   $204.40   $204.40  
  Purchase #4 $225.89   5.629%   $238.6053   $238.61   $238.60   $238.60  
  Purchase #5 $237.58   4.529%   $248.34   $248.34   $248.35   $248.30  
  Purchase #6 $59.89   9.661%   $65.676   $65.68   $65.70   $65.70  
  Purchase #7 $248.61   4.294%   $259.2853   $259.29   $259.30   $259.30  
  7 purchase totals = $1,316.19       $1,393.9410   $1,393.96   $1,394.00   $1,394.00