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 $141.58   6.524%   $150.8167   $150.82   $150.80   $150.80  
  Purchase #2 $142.49   12.692%   $160.5748   $160.57   $160.55   $160.60  
  Purchase #3 $41.50   13.400%   $47.061   $47.06   $47.05   $47.10  
  Purchase #4 $247.56   6.303%   $263.1637   $263.16   $263.15   $263.20  
  Purchase #5 $185.45   4.394%   $193.5987   $193.60   $193.60   $193.60  
  Purchase #6 $203.80   8.416%   $220.9518   $220.95   $220.95   $221.00  
  Purchase #7 $203.55   8.389%   $220.6258   $220.63   $220.65   $220.60  
  7 purchase totals = $1,165.93       $1,256.7925   $1,256.79   $1,256.75   $1,256.90