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 $238.26   7.155%   $255.3075   $255.31   $255.30   $255.30  
  Purchase #2 $43.65   10.173%   $48.0905   $48.09   $48.10   $48.10  
  Purchase #3 $113.49   7.798%   $122.34   $122.34   $122.35   $122.30  
  Purchase #4 $67.32   12.525%   $75.7518   $75.75   $75.75   $75.80  
  Purchase #5 $37.71   9.518%   $41.2992   $41.30   $41.30   $41.30  
  Purchase #6 $216.37   8.625%   $235.0319   $235.03   $235.05   $235.00  
  Purchase #7 $168.76   3.336%   $174.3898   $174.39   $174.40   $174.40  
  7 purchase totals = $885.56       $952.2107   $952.21   $952.25   $952.20