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 $175.37   11.722%   $195.9269   $195.93   $195.95   $195.90  
  Purchase #2 $154.82   12.740%   $174.5441   $174.54   $174.55   $174.50  
  Purchase #3 $170.40   8.541%   $184.9539   $184.95   $184.95   $185.00  
  Purchase #4 $9.79   7.841%   $10.5576   $10.56   $10.55   $10.60  
  Purchase #5 $55.29   11.783%   $61.8048   $61.80   $61.80   $61.80  
  Purchase #6 $146.43   6.736%   $156.2935   $156.29   $156.30   $156.30  
  Purchase #7 $116.80   12.157%   $130.9994   $131.00   $131.00   $131.00  
  7 purchase totals = $828.90       $915.0802   $915.07   $915.10   $915.10