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 $197.88   7.271%   $212.2679   $212.27   $212.25   $212.30  
  Purchase #2 $224.49   6.396%   $238.8484   $238.85   $238.85   $238.80  
  Purchase #3 $50.27   7.860%   $54.2212   $54.22   $54.20   $54.20  
  Purchase #4 $12.99   13.316%   $14.7197   $14.72   $14.70   $14.70  
  Purchase #5 $249.74   3.832%   $259.31   $259.31   $259.30   $259.30  
  Purchase #6 $169.99   5.809%   $179.8647   $179.86   $179.85   $179.90  
  Purchase #7 $212.36   6.422%   $225.9978   $226.00   $226.00   $226.00  
  7 purchase totals = $1,117.72       $1,185.2297   $1,185.23   $1,185.15   $1,185.20