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 $194.83   5.473%   $205.493   $205.49   $205.50   $205.50  
  Purchase #2 $101.86   11.583%   $113.6584   $113.66   $113.65   $113.70  
  Purchase #3 $106.39   4.443%   $111.1169   $111.12   $111.10   $111.10  
  Purchase #4 $227.31   6.560%   $242.2215   $242.22   $242.20   $242.20  
  Purchase #5 $202.55   10.265%   $223.3418   $223.34   $223.35   $223.30  
  Purchase #6 $152.91   4.609%   $159.9576   $159.96   $159.95   $160.00  
  Purchase #7 $7.41   10.689%   $8.2021   $8.20   $8.20   $8.20  
  7 purchase totals = $993.26       $1,063.9913   $1,063.99   $1,063.95   $1,064.00