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 $60.51   12.447%   $68.0417   $68.04   $68.05   $68.00  
  Purchase #2 $13.80   7.153%   $14.7871   $14.79   $14.80   $14.80  
  Purchase #3 $233.63   9.136%   $254.9744   $254.97   $254.95   $255.00  
  Purchase #4 $45.59   8.868%   $49.6329   $49.63   $49.65   $49.60  
  Purchase #5 $195.48   9.115%   $213.298   $213.30   $213.30   $213.30  
  Purchase #6 $217.61   8.149%   $235.343   $235.34   $235.35   $235.30  
  Purchase #7 $176.72   12.363%   $198.5679   $198.57   $198.55   $198.60  
  7 purchase totals = $943.34       $1,034.6450   $1,034.64   $1,034.65   $1,034.60