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 $58.26   9.495%   $63.7918   $63.79   $63.80   $63.80  
  Purchase #2 $57.82   10.305%   $63.7784   $63.78   $63.80   $63.80  
  Purchase #3 $223.89   9.443%   $245.0319   $245.03   $245.05   $245.00  
  Purchase #4 $165.31   10.427%   $182.5469   $182.55   $182.55   $182.50  
  Purchase #5 $61.73   4.765%   $64.6714   $64.67   $64.65   $64.70  
  Purchase #6 $191.52   7.285%   $205.4722   $205.47   $205.45   $205.50  
  Purchase #7 $168.76   11.458%   $188.0965   $188.10   $188.10   $188.10  
  7 purchase totals = $927.29       $1,013.3891   $1,013.39   $1,013.40   $1,013.40