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 $219.53   6.260%   $233.2726   $233.27   $233.25   $233.30  
  Purchase #2 $102.76   7.692%   $110.6643   $110.66   $110.65   $110.70  
  Purchase #3 $243.76   5.163%   $256.3453   $256.35   $256.35   $256.30  
  Purchase #4 $191.89   5.607%   $202.6493   $202.65   $202.65   $202.60  
  Purchase #5 $156.47   4.436%   $163.411   $163.41   $163.40   $163.40  
  Purchase #6 $18.90   6.838%   $20.1924   $20.19   $20.20   $20.20  
  Purchase #7 $245.67   9.521%   $269.0602   $269.06   $269.05   $269.10  
  7 purchase totals = $1,178.98       $1,255.5951   $1,255.59   $1,255.55   $1,255.60