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 $152.87   9.418%   $167.2673   $167.27   $167.25   $167.30  
  Purchase #2 $59.59   10.701%   $65.9667   $65.97   $65.95   $66.00  
  Purchase #3 $92.46   4.187%   $96.3313   $96.33   $96.35   $96.30  
  Purchase #4 $134.58   10.700%   $148.9801   $148.98   $149.00   $149.00  
  Purchase #5 $55.32   12.844%   $62.4253   $62.43   $62.45   $62.40  
  Purchase #6 $165.55   5.204%   $174.1652   $174.17   $174.15   $174.20  
  Purchase #7 $227.48   9.494%   $249.077   $249.08   $249.10   $249.10  
  7 purchase totals = $887.85       $964.2129   $964.23   $964.25   $964.30