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 $41.80   6.538%   $44.5329   $44.53   $44.55   $44.50  
  Purchase #2 $226.45   13.232%   $256.4139   $256.41   $256.40   $256.40  
  Purchase #3 $156.71   4.288%   $163.4297   $163.43   $163.45   $163.40  
  Purchase #4 $134.60   6.810%   $143.7663   $143.77   $143.75   $143.80  
  Purchase #5 $179.79   6.308%   $191.1312   $191.13   $191.15   $191.10  
  Purchase #6 $209.44   3.590%   $216.9589   $216.96   $216.95   $217.00  
  Purchase #7 $44.98   3.334%   $46.4796   $46.48   $46.50   $46.50  
  7 purchase totals = $993.77       $1,062.7125   $1,062.71   $1,062.75   $1,062.70