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 $186.69   8.411%   $202.3925   $202.39   $202.40   $202.40  
  Purchase #2 $223.55   4.523%   $233.6612   $233.66   $233.65   $233.70  
  Purchase #3 $69.27   10.832%   $76.7733   $76.77   $76.75   $76.80  
  Purchase #4 $229.31   6.698%   $244.6692   $244.67   $244.65   $244.70  
  Purchase #5 $150.40   7.431%   $161.5762   $161.58   $161.60   $161.60  
  Purchase #6 $193.98   8.227%   $209.9387   $209.94   $209.95   $209.90  
  Purchase #7 $201.68   10.562%   $222.9814   $222.98   $223.00   $223.00  
  7 purchase totals = $1,254.88       $1,351.9925   $1,351.99   $1,352.00   $1,352.10