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 $105.65   12.818%   $119.1922   $119.19   $119.20   $119.20  
  Purchase #2 $229.84   6.446%   $244.6555   $244.66   $244.65   $244.70  
  Purchase #3 $27.37   6.198%   $29.0664   $29.07   $29.05   $29.10  
  Purchase #4 $37.44   11.299%   $41.6703   $41.67   $41.65   $41.70  
  Purchase #5 $159.70   12.198%   $179.1802   $179.18   $179.20   $179.20  
  Purchase #6 $214.27   13.551%   $243.3057   $243.31   $243.30   $243.30  
  Purchase #7 $244.67   5.283%   $257.5959   $257.60   $257.60   $257.60  
  7 purchase totals = $1,018.94       $1,114.6662   $1,114.68   $1,114.65   $1,114.80