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 $141.77   6.475%   $150.9496   $150.95   $150.95   $150.90  
  Purchase #2 $93.25   5.783%   $98.6426   $98.64   $98.65   $98.60  
  Purchase #3 $181.94   9.168%   $198.6203   $198.62   $198.60   $198.60  
  Purchase #4 $99.94   7.751%   $107.6863   $107.69   $107.70   $107.70  
  Purchase #5 $181.40   7.194%   $194.4499   $194.45   $194.45   $194.40  
  Purchase #6 $134.88   13.435%   $153.0011   $153.00   $153.00   $153.00  
  Purchase #7 $115.95   13.163%   $131.2125   $131.21   $131.20   $131.20  
  7 purchase totals = $949.13       $1,034.5623   $1,034.56   $1,034.55   $1,034.40