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 $103.61   13.723%   $117.8284   $117.83   $117.85   $117.80  
  Purchase #2 $67.84   12.593%   $76.3831   $76.38   $76.40   $76.40  
  Purchase #3 $83.27   5.148%   $87.5567   $87.56   $87.55   $87.60  
  Purchase #4 $228.78   7.584%   $246.1307   $246.13   $246.15   $246.10  
  Purchase #5 $208.95   10.312%   $230.4969   $230.50   $230.50   $230.50  
  Purchase #6 $116.80   5.716%   $123.4763   $123.48   $123.50   $123.50  
  Purchase #7 $150.75   6.590%   $160.6844   $160.68   $160.70   $160.70  
  7 purchase totals = $960.00       $1,042.5565   $1,042.56   $1,042.65   $1,042.60