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 $164.95   13.175%   $186.6822   $186.68   $186.70   $186.70  
  Purchase #2 $122.85   8.247%   $132.9814   $132.98   $133.00   $133.00  
  Purchase #3 $115.92   6.738%   $123.7307   $123.73   $123.75   $123.70  
  Purchase #4 $204.81   3.765%   $212.5211   $212.52   $212.50   $212.50  
  Purchase #5 $137.67   9.762%   $151.1093   $151.11   $151.10   $151.10  
  Purchase #6 $202.27   3.411%   $209.1694   $209.17   $209.15   $209.20  
  Purchase #7 $244.82   3.424%   $253.2026   $253.20   $253.20   $253.20  
  7 purchase totals = $1,193.29       $1,269.3967   $1,269.39   $1,269.40   $1,269.40