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 $202.32   4.146%   $210.7082   $210.71   $210.70   $210.70  
  Purchase #2 $148.93   12.190%   $167.0846   $167.08   $167.10   $167.10  
  Purchase #3 $119.39   10.752%   $132.2268   $132.23   $132.25   $132.20  
  Purchase #4 $78.59   6.691%   $83.8485   $83.85   $83.85   $83.80  
  Purchase #5 $201.74   13.357%   $228.6864   $228.69   $228.70   $228.70  
  Purchase #6 $69.78   9.217%   $76.2116   $76.21   $76.20   $76.20  
  Purchase #7 $59.33   4.419%   $61.9518   $61.95   $61.95   $62.00  
  7 purchase totals = $880.08       $960.7179   $960.72   $960.75   $960.70