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 $151.82   10.837%   $168.2727   $168.27   $168.25   $168.30  
  Purchase #2 $33.62   10.642%   $37.1978   $37.20   $37.20   $37.20  
  Purchase #3 $85.73   7.195%   $91.8983   $91.90   $91.90   $91.90  
  Purchase #4 $111.32   8.750%   $121.0605   $121.06   $121.05   $121.10  
  Purchase #5 $205.98   6.319%   $218.9959   $219.00   $219.00   $219.00  
  Purchase #6 $122.77   13.551%   $139.4066   $139.41   $139.40   $139.40  
  Purchase #7 $237.80   11.138%   $264.2862   $264.29   $264.30   $264.30  
  7 purchase totals = $949.04       $1,041.1180   $1,041.13   $1,041.10   $1,041.20