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 $216.40   5.614%   $228.5487   $228.55   $228.55   $228.50  
  Purchase #2 $90.30   9.150%   $98.5625   $98.56   $98.55   $98.60  
  Purchase #3 $231.89   4.302%   $241.8659   $241.87   $241.85   $241.90  
  Purchase #4 $165.50   5.243%   $174.1772   $174.18   $174.20   $174.20  
  Purchase #5 $247.48   11.807%   $276.7   $276.70   $276.70   $276.70  
  Purchase #6 $8.33   5.174%   $8.761   $8.76   $8.75   $8.80  
  Purchase #7 $118.38   11.792%   $132.3394   $132.34   $132.35   $132.30  
  7 purchase totals = $1,078.28       $1,160.9547   $1,160.96   $1,160.95   $1,161.00