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 $250.33   5.409%   $263.8703   $263.87   $263.85   $263.90  
  Purchase #2 $111.69   13.390%   $126.6453   $126.65   $126.65   $126.60  
  Purchase #3 $46.40   12.148%   $52.0367   $52.04   $52.05   $52.00  
  Purchase #4 $37.29   10.199%   $41.0932   $41.09   $41.10   $41.10  
  Purchase #5 $222.34   6.837%   $237.5414   $237.54   $237.55   $237.50  
  Purchase #6 $160.88   6.479%   $171.3034   $171.30   $171.30   $171.30  
  Purchase #7 $66.36   13.390%   $75.2456   $75.25   $75.25   $75.20  
  7 purchase totals = $895.29       $967.7359   $967.74   $967.75   $967.60