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 $195.54   5.584%   $206.459   $206.46   $206.45   $206.50  
  Purchase #2 $239.48   7.226%   $256.7848   $256.78   $256.80   $256.80  
  Purchase #3 $248.88   9.465%   $272.4365   $272.44   $272.45   $272.40  
  Purchase #4 $55.59   9.114%   $60.6565   $60.66   $60.65   $60.70  
  Purchase #5 $98.60   9.355%   $107.824   $107.82   $107.80   $107.80  
  Purchase #6 $155.25   7.772%   $167.316   $167.32   $167.30   $167.30  
  Purchase #7 $90.79   9.818%   $99.7038   $99.70   $99.70   $99.70  
  7 purchase totals = $1,084.13       $1,171.1806   $1,171.18   $1,171.15   $1,171.20