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 $166.36   9.796%   $182.6566   $182.66   $182.65   $182.70  
  Purchase #2 $60.68   11.119%   $67.427   $67.43   $67.45   $67.40  
  Purchase #3 $96.39   13.381%   $109.2879   $109.29   $109.30   $109.30  
  Purchase #4 $248.80   10.587%   $275.1405   $275.14   $275.15   $275.10  
  Purchase #5 $104.62   6.277%   $111.187   $111.19   $111.20   $111.20  
  Purchase #6 $218.33   11.661%   $243.7895   $243.79   $243.80   $243.80  
  Purchase #7 $7.88   13.561%   $8.9486   $8.95   $8.95   $8.90  
  7 purchase totals = $903.06       $998.4371   $998.45   $998.50   $998.40