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 $54.51   7.582%   $58.6429   $58.64   $58.65   $58.60  
  Purchase #2 $83.46   3.402%   $86.2993   $86.30   $86.30   $86.30  
  Purchase #3 $191.52   4.275%   $199.7075   $199.71   $199.70   $199.70  
  Purchase #4 $240.80   10.442%   $265.9443   $265.94   $265.95   $265.90  
  Purchase #5 $172.70   7.142%   $185.0342   $185.03   $185.05   $185.00  
  Purchase #6 $8.40   11.295%   $9.3488   $9.35   $9.35   $9.30  
  Purchase #7 $181.48   11.624%   $202.5752   $202.58   $202.60   $202.60  
  7 purchase totals = $932.87       $1,007.5522   $1,007.55   $1,007.60   $1,007.40