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 $181.69   12.596%   $204.5757   $204.58   $204.60   $204.60  
  Purchase #2 $69.79   7.323%   $74.9007   $74.90   $74.90   $74.90  
  Purchase #3 $219.39   3.768%   $227.6566   $227.66   $227.65   $227.70  
  Purchase #4 $117.32   4.659%   $122.7859   $122.79   $122.80   $122.80  
  Purchase #5 $93.59   9.740%   $102.7057   $102.71   $102.70   $102.70  
  Purchase #6 $187.71   4.272%   $195.729   $195.73   $195.75   $195.70  
  Purchase #7 $144.74   4.445%   $151.1737   $151.17   $151.15   $151.20  
  7 purchase totals = $1,014.23       $1,079.5273   $1,079.54   $1,079.55   $1,079.60