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 $161.75   13.302%   $183.266   $183.27   $183.25   $183.30  
  Purchase #2 $140.33   7.514%   $150.8744   $150.87   $150.85   $150.90  
  Purchase #3 $230.90   5.746%   $244.1675   $244.17   $244.15   $244.20  
  Purchase #4 $212.50   3.448%   $219.827   $219.83   $219.85   $219.80  
  Purchase #5 $46.27   4.231%   $48.2277   $48.23   $48.25   $48.20  
  Purchase #6 $236.53   6.568%   $252.0653   $252.07   $252.05   $252.10  
  Purchase #7 $204.54   4.573%   $213.8936   $213.89   $213.90   $213.90  
  7 purchase totals = $1,232.82       $1,312.3215   $1,312.33   $1,312.30   $1,312.40