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 $175.32   12.710%   $197.6032   $197.60   $197.60   $197.60  
  Purchase #2 $24.50   9.804%   $26.902   $26.90   $26.90   $26.90  
  Purchase #3 $230.27   11.251%   $256.1777   $256.18   $256.20   $256.20  
  Purchase #4 $36.93   12.781%   $41.65   $41.65   $41.65   $41.70  
  Purchase #5 $199.95   7.499%   $214.9443   $214.94   $214.95   $214.90  
  Purchase #6 $97.80   11.786%   $109.3267   $109.33   $109.35   $109.30  
  Purchase #7 $229.45   9.201%   $250.5617   $250.56   $250.55   $250.60  
  7 purchase totals = $994.22       $1,097.1656   $1,097.16   $1,097.20   $1,097.20