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 $52.39   12.544%   $58.9618   $58.96   $58.95   $59.00  
  Purchase #2 $155.84   6.643%   $166.1925   $166.19   $166.20   $166.20  
  Purchase #3 $52.84   5.706%   $55.8551   $55.86   $55.85   $55.90  
  Purchase #4 $245.28   9.235%   $267.9316   $267.93   $267.95   $267.90  
  Purchase #5 $69.78   5.619%   $73.7009   $73.70   $73.70   $73.70  
  Purchase #6 $145.76   3.234%   $150.4739   $150.47   $150.45   $150.50  
  Purchase #7 $76.77   4.569%   $80.2776   $80.28   $80.30   $80.30  
  7 purchase totals = $798.66       $853.3934   $853.39   $853.40   $853.50