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 $61.69   8.124%   $66.7017   $66.70   $66.70   $66.70  
  Purchase #2 $139.49   13.624%   $158.4941   $158.49   $158.50   $158.50  
  Purchase #3 $111.88   7.454%   $120.2195   $120.22   $120.20   $120.20  
  Purchase #4 $126.63   11.690%   $141.433   $141.43   $141.45   $141.40  
  Purchase #5 $131.51   10.745%   $145.6407   $145.64   $145.65   $145.60  
  Purchase #6 $5.45   7.751%   $5.8724   $5.87   $5.85   $5.90  
  Purchase #7 $227.88   3.257%   $235.3021   $235.30   $235.30   $235.30  
  7 purchase totals = $804.53       $873.6635   $873.65   $873.65   $873.60