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 $241.65   8.358%   $261.8471   $261.85   $261.85   $261.80  
  Purchase #2 $6.52   11.757%   $7.2866   $7.29   $7.30   $7.30  
  Purchase #3 $31.66   12.519%   $35.6235   $35.62   $35.60   $35.60  
  Purchase #4 $57.84   11.768%   $64.6466   $64.65   $64.65   $64.60  
  Purchase #5 $128.68   5.482%   $135.7342   $135.73   $135.75   $135.70  
  Purchase #6 $222.96   9.830%   $244.877   $244.88   $244.90   $244.90  
  Purchase #7 $232.32   11.315%   $258.607   $258.61   $258.60   $258.60  
  7 purchase totals = $921.63       $1,008.6220   $1,008.63   $1,008.65   $1,008.50