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 $86.45   11.657%   $96.5275   $96.53   $96.55   $96.50  
  Purchase #2 $154.98   4.281%   $161.6147   $161.61   $161.60   $161.60  
  Purchase #3 $147.39   3.333%   $152.3025   $152.30   $152.30   $152.30  
  Purchase #4 $55.50   5.126%   $58.3449   $58.34   $58.35   $58.30  
  Purchase #5 $49.26   5.763%   $52.0989   $52.10   $52.10   $52.10  
  Purchase #6 $152.55   12.562%   $171.7133   $171.71   $171.70   $171.70  
  Purchase #7 $6.98   3.850%   $7.2487   $7.25   $7.25   $7.20  
  7 purchase totals = $653.11       $699.8505   $699.84   $699.85   $699.70