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 $63.36   7.696%   $68.2362   $68.24   $68.25   $68.20  
  Purchase #2 $161.39   3.767%   $167.4696   $167.47   $167.45   $167.50  
  Purchase #3 $158.90   12.689%   $179.0628   $179.06   $179.05   $179.10  
  Purchase #4 $249.99   10.140%   $275.339   $275.34   $275.35   $275.30  
  Purchase #5 $232.64   9.667%   $255.1293   $255.13   $255.15   $255.10  
  Purchase #6 $165.46   13.217%   $187.3288   $187.33   $187.35   $187.30  
  Purchase #7 $237.72   3.843%   $246.8556   $246.86   $246.85   $246.90  
  7 purchase totals = $1,269.46       $1,379.4213   $1,379.43   $1,379.45   $1,379.40