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 $59.82   9.283%   $65.3731   $65.37   $65.35   $65.40  
  Purchase #2 $232.66   10.487%   $257.0591   $257.06   $257.05   $257.10  
  Purchase #3 $225.50   5.341%   $237.544   $237.54   $237.55   $237.50  
  Purchase #4 $181.83   11.275%   $202.3313   $202.33   $202.35   $202.30  
  Purchase #5 $123.73   11.265%   $137.6682   $137.67   $137.65   $137.70  
  Purchase #6 $30.33   3.408%   $31.3636   $31.36   $31.35   $31.40  
  Purchase #7 $97.70   3.695%   $101.31   $101.31   $101.30   $101.30  
  7 purchase totals = $951.57       $1,032.6493   $1,032.64   $1,032.60   $1,032.70