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 $190.94   7.209%   $204.7049   $204.70   $204.70   $204.70  
  Purchase #2 $68.71   4.764%   $71.9833   $71.98   $72.00   $72.00  
  Purchase #3 $122.74   8.188%   $132.79   $132.79   $132.80   $132.80  
  Purchase #4 $63.45   11.742%   $70.9003   $70.90   $70.90   $70.90  
  Purchase #5 $75.74   7.751%   $81.6106   $81.61   $81.60   $81.60  
  Purchase #6 $89.57   5.565%   $94.5546   $94.55   $94.55   $94.60  
  Purchase #7 $213.43   10.116%   $235.0206   $235.02   $235.00   $235.00  
  7 purchase totals = $824.58       $891.5643   $891.55   $891.55   $891.60