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 $46.46   13.741%   $52.8441   $52.84   $52.85   $52.80  
  Purchase #2 $241.85   11.194%   $268.9227   $268.92   $268.90   $268.90  
  Purchase #3 $216.60   11.580%   $241.6823   $241.68   $241.70   $241.70  
  Purchase #4 $108.89   11.364%   $121.2643   $121.26   $121.25   $121.30  
  Purchase #5 $200.29   12.642%   $225.6107   $225.61   $225.60   $225.60  
  Purchase #6 $227.55   4.381%   $237.519   $237.52   $237.50   $237.50  
  Purchase #7 $154.82   7.820%   $166.9269   $166.93   $166.95   $166.90  
  7 purchase totals = $1,196.46       $1,314.7700   $1,314.76   $1,314.75   $1,314.70