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 $246.97   10.259%   $272.3067   $272.31   $272.30   $272.30  
  Purchase #2 $50.94   6.526%   $54.2643   $54.26   $54.25   $54.30  
  Purchase #3 $101.29   10.110%   $111.5304   $111.53   $111.55   $111.50  
  Purchase #4 $209.79   9.468%   $229.6529   $229.65   $229.65   $229.70  
  Purchase #5 $7.54   5.482%   $7.9533   $7.95   $7.95   $8.00  
  Purchase #6 $226.53   11.153%   $251.7949   $251.79   $251.80   $251.80  
  Purchase #7 $225.83   12.318%   $253.6477   $253.65   $253.65   $253.60  
  7 purchase totals = $1,068.89       $1,181.1502   $1,181.14   $1,181.15   $1,181.20