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 $193.29   4.677%   $202.3302   $202.33   $202.35   $202.30  
  Purchase #2 $110.99   13.659%   $126.1501   $126.15   $126.15   $126.20  
  Purchase #3 $131.36   12.425%   $147.6815   $147.68   $147.70   $147.70  
  Purchase #4 $229.50   6.678%   $244.826   $244.83   $244.85   $244.80  
  Purchase #5 $226.67   5.148%   $238.339   $238.34   $238.35   $238.30  
  Purchase #6 $66.30   11.203%   $73.7276   $73.73   $73.75   $73.70  
  Purchase #7 $232.93   12.491%   $262.0253   $262.03   $262.05   $262.00  
  7 purchase totals = $1,191.04       $1,295.0797   $1,295.09   $1,295.20   $1,295.00