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 $54.53   8.682%   $59.2643   $59.26   $59.25   $59.30  
  Purchase #2 $107.46   7.649%   $115.6796   $115.68   $115.70   $115.70  
  Purchase #3 $145.51   13.720%   $165.474   $165.47   $165.45   $165.50  
  Purchase #4 $171.39   9.865%   $188.2976   $188.30   $188.30   $188.30  
  Purchase #5 $210.72   9.610%   $230.9702   $230.97   $230.95   $231.00  
  Purchase #6 $43.31   11.841%   $48.4383   $48.44   $48.45   $48.40  
  Purchase #7 $207.80   11.643%   $231.9942   $231.99   $232.00   $232.00  
  7 purchase totals = $940.72       $1,040.1182   $1,040.11   $1,040.10   $1,040.20