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 $49.63   9.409%   $54.2997   $54.30   $54.30   $54.30  
  Purchase #2 $211.40   4.221%   $220.3232   $220.32   $220.30   $220.30  
  Purchase #3 $155.30   12.671%   $174.9781   $174.98   $175.00   $175.00  
  Purchase #4 $246.52   10.757%   $273.0382   $273.04   $273.05   $273.00  
  Purchase #5 $55.35   13.765%   $62.9689   $62.97   $62.95   $63.00  
  Purchase #6 $16.60   7.828%   $17.8994   $17.90   $17.90   $17.90  
  Purchase #7 $236.56   11.138%   $262.9081   $262.91   $262.90   $262.90  
  7 purchase totals = $971.36       $1,066.4156   $1,066.42   $1,066.40   $1,066.40