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 $164.66   10.207%   $181.4668   $181.47   $181.45   $181.50  
  Purchase #2 $245.85   9.618%   $269.4959   $269.50   $269.50   $269.50  
  Purchase #3 $119.49   6.354%   $127.0824   $127.08   $127.10   $127.10  
  Purchase #4 $183.64   5.655%   $194.0248   $194.02   $194.00   $194.00  
  Purchase #5 $209.42   5.425%   $220.781   $220.78   $220.80   $220.80  
  Purchase #6 $141.60   6.774%   $151.192   $151.19   $151.20   $151.20  
  Purchase #7 $228.89   9.438%   $250.4926   $250.49   $250.50   $250.50  
  7 purchase totals = $1,293.55       $1,394.5355   $1,394.53   $1,394.55   $1,394.60