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 $77.77   11.590%   $86.7835   $86.78   $86.80   $86.80  
  Purchase #2 $230.73   5.179%   $242.6795   $242.68   $242.70   $242.70  
  Purchase #3 $136.88   11.120%   $152.1011   $152.10   $152.10   $152.10  
  Purchase #4 $189.49   9.534%   $207.556   $207.56   $207.55   $207.60  
  Purchase #5 $173.35   12.476%   $194.9771   $194.98   $195.00   $195.00  
  Purchase #6 $44.32   3.490%   $45.8668   $45.87   $45.85   $45.90  
  Purchase #7 $75.46   8.660%   $81.9948   $81.99   $82.00   $82.00  
  7 purchase totals = $928.00       $1,011.9588   $1,011.96   $1,012.00   $1,012.10