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 $52.64   11.274%   $58.5746   $58.57   $58.55   $58.60  
  Purchase #2 $189.27   9.607%   $207.4532   $207.45   $207.45   $207.50  
  Purchase #3 $225.95   13.628%   $256.7425   $256.74   $256.75   $256.70  
  Purchase #4 $210.37   13.434%   $238.6311   $238.63   $238.65   $238.60  
  Purchase #5 $107.25   8.161%   $116.0027   $116.00   $116.00   $116.00  
  Purchase #6 $57.35   6.437%   $61.0416   $61.04   $61.05   $61.00  
  Purchase #7 $212.46   5.527%   $224.2027   $224.20   $224.20   $224.20  
  7 purchase totals = $1,055.29       $1,162.6484   $1,162.63   $1,162.65   $1,162.60