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 $75.93   12.228%   $85.2147   $85.21   $85.20   $85.20  
  Purchase #2 $149.65   8.201%   $161.9228   $161.92   $161.90   $161.90  
  Purchase #3 $152.73   9.469%   $167.192   $167.19   $167.20   $167.20  
  Purchase #4 $208.32   12.626%   $234.6225   $234.62   $234.60   $234.60  
  Purchase #5 $196.91   12.572%   $221.6655   $221.67   $221.65   $221.70  
  Purchase #6 $248.81   10.823%   $275.7387   $275.74   $275.75   $275.70  
  Purchase #7 $225.33   4.661%   $235.8326   $235.83   $235.85   $235.80  
  7 purchase totals = $1,257.68       $1,382.1888   $1,382.18   $1,382.15   $1,382.10