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 $203.71   11.398%   $226.9289   $226.93   $226.95   $226.90  
  Purchase #2 $40.95   10.836%   $45.3873   $45.39   $45.40   $45.40  
  Purchase #3 $157.70   8.598%   $171.259   $171.26   $171.25   $171.30  
  Purchase #4 $201.68   13.278%   $228.4591   $228.46   $228.45   $228.50  
  Purchase #5 $219.71   3.121%   $226.5671   $226.57   $226.55   $226.60  
  Purchase #6 $84.93   9.287%   $92.8174   $92.82   $92.80   $92.80  
  Purchase #7 $10.97   13.342%   $12.4336   $12.43   $12.45   $12.40  
  7 purchase totals = $919.65       $1,003.8524   $1,003.86   $1,003.85   $1,003.90