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 $243.44   6.536%   $259.3512   $259.35   $259.35   $259.40  
  Purchase #2 $126.49   3.306%   $130.6718   $130.67   $130.65   $130.70  
  Purchase #3 $85.52   10.428%   $94.438   $94.44   $94.45   $94.40  
  Purchase #4 $72.52   11.779%   $81.0621   $81.06   $81.05   $81.10  
  Purchase #5 $82.88   7.868%   $89.401   $89.40   $89.40   $89.40  
  Purchase #6 $193.65   3.110%   $199.6725   $199.67   $199.65   $199.70  
  Purchase #7 $159.29   3.850%   $165.4227   $165.42   $165.40   $165.40  
  7 purchase totals = $963.79       $1,020.0193   $1,020.01   $1,019.95   $1,020.10