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 $183.50   10.370%   $202.529   $202.53   $202.55   $202.50  
  Purchase #2 $59.84   4.762%   $62.6896   $62.69   $62.70   $62.70  
  Purchase #3 $232.66   13.248%   $263.4828   $263.48   $263.50   $263.50  
  Purchase #4 $168.37   11.701%   $188.071   $188.07   $188.05   $188.10  
  Purchase #5 $80.43   12.612%   $90.5738   $90.57   $90.55   $90.60  
  Purchase #6 $177.65   11.216%   $197.5752   $197.58   $197.60   $197.60  
  Purchase #7 $245.45   4.464%   $256.4069   $256.41   $256.40   $256.40  
  7 purchase totals = $1,147.90       $1,261.3283   $1,261.33   $1,261.35   $1,261.40