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 $54.71   8.541%   $59.3828   $59.38   $59.40   $59.40  
  Purchase #2 $233.60   8.236%   $252.8393   $252.84   $252.85   $252.80  
  Purchase #3 $26.56   3.407%   $27.4649   $27.46   $27.45   $27.50  
  Purchase #4 $203.25   4.333%   $212.0568   $212.06   $212.05   $212.10  
  Purchase #5 $215.62   7.629%   $232.0696   $232.07   $232.05   $232.10  
  Purchase #6 $47.70   6.182%   $50.6488   $50.65   $50.65   $50.60  
  Purchase #7 $53.44   9.468%   $58.4997   $58.50   $58.50   $58.50  
  7 purchase totals = $834.88       $892.9619   $892.96   $892.95   $893.00