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 $39.44   3.625%   $40.8697   $40.87   $40.85   $40.90  
  Purchase #2 $200.84   4.637%   $210.153   $210.15   $210.15   $210.20  
  Purchase #3 $120.90   7.134%   $129.525   $129.53   $129.55   $129.50  
  Purchase #4 $200.96   9.501%   $220.0532   $220.05   $220.05   $220.10  
  Purchase #5 $142.82   9.490%   $156.3736   $156.37   $156.35   $156.40  
  Purchase #6 $134.76   5.551%   $142.2405   $142.24   $142.25   $142.20  
  Purchase #7 $238.29   3.863%   $247.4951   $247.50   $247.50   $247.50  
  7 purchase totals = $1,078.01       $1,146.7101   $1,146.71   $1,146.70   $1,146.80