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 $61.98   13.338%   $70.2469   $70.25   $70.25   $70.20  
  Purchase #2 $228.29   4.140%   $237.7412   $237.74   $237.75   $237.70  
  Purchase #3 $63.68   7.574%   $68.5031   $68.50   $68.50   $68.50  
  Purchase #4 $202.34   11.666%   $225.945   $225.95   $225.95   $225.90  
  Purchase #5 $93.76   13.657%   $106.5648   $106.56   $106.55   $106.60  
  Purchase #6 $195.92   8.649%   $212.8651   $212.87   $212.85   $212.90  
  Purchase #7 $161.85   6.269%   $171.9964   $172.00   $172.00   $172.00  
  7 purchase totals = $1,007.82       $1,093.8625   $1,093.87   $1,093.85   $1,093.80