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 $218.74   11.444%   $243.7726   $243.77   $243.75   $243.80  
  Purchase #2 $55.50   6.529%   $59.1236   $59.12   $59.10   $59.10  
  Purchase #3 $153.29   6.292%   $162.935   $162.94   $162.95   $162.90  
  Purchase #4 $242.72   4.808%   $254.39   $254.39   $254.40   $254.40  
  Purchase #5 $218.75   4.551%   $228.7053   $228.71   $228.70   $228.70  
  Purchase #6 $246.33   4.425%   $257.2301   $257.23   $257.25   $257.20  
  Purchase #7 $195.87   12.720%   $220.7847   $220.78   $220.80   $220.80  
  7 purchase totals = $1,331.20       $1,426.9413   $1,426.94   $1,426.95   $1,426.90