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 $224.36   11.756%   $250.7358   $250.74   $250.75   $250.70  
  Purchase #2 $211.87   12.817%   $239.0254   $239.03   $239.05   $239.00  
  Purchase #3 $44.53   7.120%   $47.7005   $47.70   $47.70   $47.70  
  Purchase #4 $247.86   6.183%   $263.1852   $263.19   $263.20   $263.20  
  Purchase #5 $111.70   5.630%   $117.9887   $117.99   $118.00   $118.00  
  Purchase #6 $163.60   9.340%   $178.8802   $178.88   $178.90   $178.90  
  Purchase #7 $26.60   5.203%   $27.984   $27.98   $28.00   $28.00  
  7 purchase totals = $1,030.52       $1,125.4998   $1,125.51   $1,125.60   $1,125.50