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 $188.75   10.273%   $208.1403   $208.14   $208.15   $208.10  
  Purchase #2 $131.55   12.285%   $147.7109   $147.71   $147.70   $147.70  
  Purchase #3 $228.73   6.620%   $243.8719   $243.87   $243.85   $243.90  
  Purchase #4 $182.87   7.328%   $196.2707   $196.27   $196.25   $196.30  
  Purchase #5 $31.29   10.753%   $34.6546   $34.65   $34.65   $34.70  
  Purchase #6 $118.86   11.869%   $132.9675   $132.97   $132.95   $133.00  
  Purchase #7 $45.68   5.343%   $48.1207   $48.12   $48.10   $48.10  
  7 purchase totals = $927.73       $1,011.7366   $1,011.73   $1,011.65   $1,011.80