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 $61.69   10.367%   $68.0854   $68.09   $68.10   $68.10  
  Purchase #2 $202.50   6.677%   $216.0209   $216.02   $216.00   $216.00  
  Purchase #3 $142.66   5.840%   $150.9913   $150.99   $151.00   $151.00  
  Purchase #4 $169.72   10.596%   $187.7035   $187.70   $187.70   $187.70  
  Purchase #5 $209.80   11.236%   $233.3731   $233.37   $233.35   $233.40  
  Purchase #6 $66.70   9.412%   $72.9778   $72.98   $73.00   $73.00  
  Purchase #7 $74.30   5.629%   $78.4823   $78.48   $78.50   $78.50  
  7 purchase totals = $927.37       $1,007.6343   $1,007.63   $1,007.65   $1,007.70