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 $206.43   12.527%   $232.2895   $232.29   $232.30   $232.30  
  Purchase #2 $98.37   12.298%   $110.4675   $110.47   $110.45   $110.50  
  Purchase #3 $58.71   4.126%   $61.1324   $61.13   $61.15   $61.10  
  Purchase #4 $206.66   9.703%   $226.7122   $226.71   $226.70   $226.70  
  Purchase #5 $11.79   7.277%   $12.648   $12.65   $12.65   $12.60  
  Purchase #6 $230.76   10.846%   $255.7882   $255.79   $255.80   $255.80  
  Purchase #7 $153.61   9.219%   $167.7713   $167.77   $167.75   $167.80  
  7 purchase totals = $966.33       $1,066.8091   $1,066.81   $1,066.80   $1,066.80