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 $211.92   3.503%   $219.3436   $219.34   $219.35   $219.30  
  Purchase #2 $113.71   5.439%   $119.8947   $119.89   $119.90   $119.90  
  Purchase #3 $129.36   9.162%   $141.212   $141.21   $141.20   $141.20  
  Purchase #4 $210.78   7.328%   $226.226   $226.23   $226.25   $226.20  
  Purchase #5 $79.25   11.470%   $88.34   $88.34   $88.35   $88.30  
  Purchase #6 $199.78   5.534%   $210.8358   $210.84   $210.85   $210.80  
  Purchase #7 $12.64   8.163%   $13.6718   $13.67   $13.65   $13.70  
  7 purchase totals = $957.44       $1,019.5239   $1,019.52   $1,019.55   $1,019.40