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 $191.37   6.168%   $203.1737   $203.17   $203.15   $203.20  
  Purchase #2 $239.99   13.860%   $273.2526   $273.25   $273.25   $273.30  
  Purchase #3 $210.60   6.835%   $224.9945   $224.99   $225.00   $225.00  
  Purchase #4 $235.49   6.860%   $251.6446   $251.64   $251.65   $251.60  
  Purchase #5 $82.77   5.127%   $87.0136   $87.01   $87.00   $87.00  
  Purchase #6 $58.61   12.826%   $66.1273   $66.13   $66.15   $66.10  
  Purchase #7 $102.61   13.684%   $116.6512   $116.65   $116.65   $116.70  
  7 purchase totals = $1,121.44       $1,222.8575   $1,222.84   $1,222.85   $1,222.90