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 $248.53   3.240%   $256.5824   $256.58   $256.60   $256.60  
  Purchase #2 $82.43   11.681%   $92.0586   $92.06   $92.05   $92.10  
  Purchase #3 $85.50   5.157%   $89.9092   $89.91   $89.90   $89.90  
  Purchase #4 $77.71   6.743%   $82.95   $82.95   $82.95   $83.00  
  Purchase #5 $109.72   10.742%   $121.5061   $121.51   $121.50   $121.50  
  Purchase #6 $188.94   9.735%   $207.3333   $207.33   $207.35   $207.30  
  Purchase #7 $193.62   4.320%   $201.9844   $201.98   $202.00   $202.00  
  7 purchase totals = $986.45       $1,052.3240   $1,052.32   $1,052.35   $1,052.40