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 $117.83   4.818%   $123.507   $123.51   $123.50   $123.50  
  Purchase #2 $121.59   11.662%   $135.7698   $135.77   $135.75   $135.80  
  Purchase #3 $246.66   6.400%   $262.4462   $262.45   $262.45   $262.40  
  Purchase #4 $88.53   10.170%   $97.5335   $97.53   $97.55   $97.50  
  Purchase #5 $109.70   10.717%   $121.4565   $121.46   $121.45   $121.50  
  Purchase #6 $199.80   11.515%   $222.807   $222.81   $222.80   $222.80  
  Purchase #7 $177.98   11.781%   $198.9478   $198.95   $198.95   $198.90  
  7 purchase totals = $1,062.09       $1,162.4678   $1,162.48   $1,162.45   $1,162.40