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 $139.37   9.559%   $152.6924   $152.69   $152.70   $152.70  
  Purchase #2 $157.29   6.585%   $167.6475   $167.65   $167.65   $167.60  
  Purchase #3 $99.39   3.257%   $102.6271   $102.63   $102.65   $102.60  
  Purchase #4 $81.68   13.109%   $92.3874   $92.39   $92.40   $92.40  
  Purchase #5 $118.72   8.273%   $128.5417   $128.54   $128.55   $128.50  
  Purchase #6 $138.93   11.203%   $154.4943   $154.49   $154.50   $154.50  
  Purchase #7 $221.49   10.787%   $245.3821   $245.38   $245.40   $245.40  
  7 purchase totals = $956.87       $1,043.7725   $1,043.77   $1,043.85   $1,043.70