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 $45.91   13.149%   $51.9467   $51.95   $51.95   $51.90  
  Purchase #2 $183.31   11.686%   $204.7316   $204.73   $204.75   $204.70  
  Purchase #3 $45.58   13.614%   $51.7853   $51.79   $51.80   $51.80  
  Purchase #4 $175.55   11.472%   $195.6891   $195.69   $195.70   $195.70  
  Purchase #5 $248.36   6.813%   $265.2808   $265.28   $265.30   $265.30  
  Purchase #6 $137.75   6.231%   $146.3332   $146.33   $146.35   $146.30  
  Purchase #7 $175.98   13.519%   $199.7707   $199.77   $199.75   $199.80  
  7 purchase totals = $1,012.44       $1,115.5374   $1,115.54   $1,115.60   $1,115.50