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 $74.38   12.113%   $83.3896   $83.39   $83.40   $83.40  
  Purchase #2 $220.27   8.366%   $238.6978   $238.70   $238.70   $238.70  
  Purchase #3 $180.43   7.214%   $193.4462   $193.45   $193.45   $193.40  
  Purchase #4 $202.66   7.855%   $218.5789   $218.58   $218.60   $218.60  
  Purchase #5 $247.71   6.391%   $263.5411   $263.54   $263.55   $263.50  
  Purchase #6 $102.96   7.405%   $110.5842   $110.58   $110.60   $110.60  
  Purchase #7 $194.71   11.441%   $216.9868   $216.99   $217.00   $217.00  
  7 purchase totals = $1,223.12       $1,325.2246   $1,325.23   $1,325.30   $1,325.20