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 $114.69   6.391%   $122.0198   $122.02   $122.00   $122.00  
  Purchase #2 $214.43   13.810%   $244.0428   $244.04   $244.05   $244.00  
  Purchase #3 $185.57   5.538%   $195.8469   $195.85   $195.85   $195.80  
  Purchase #4 $45.38   5.520%   $47.885   $47.89   $47.90   $47.90  
  Purchase #5 $129.61   6.698%   $138.2913   $138.29   $138.30   $138.30  
  Purchase #6 $56.29   5.615%   $59.4507   $59.45   $59.45   $59.50  
  Purchase #7 $194.55   6.424%   $207.0479   $207.05   $207.05   $207.00  
  7 purchase totals = $940.52       $1,014.5844   $1,014.59   $1,014.60   $1,014.50