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 $248.41   13.142%   $281.056   $281.06   $281.05   $281.10  
  Purchase #2 $211.35   12.640%   $238.0646   $238.06   $238.05   $238.10  
  Purchase #3 $87.67   8.175%   $94.837   $94.84   $94.85   $94.80  
  Purchase #4 $150.26   11.628%   $167.7322   $167.73   $167.75   $167.70  
  Purchase #5 $121.58   5.238%   $127.9484   $127.95   $127.95   $127.90  
  Purchase #6 $13.35   4.282%   $13.9216   $13.92   $13.90   $13.90  
  Purchase #7 $142.91   13.310%   $161.9313   $161.93   $161.95   $161.90  
  7 purchase totals = $975.53       $1,085.4911   $1,085.49   $1,085.50   $1,085.40