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 $250.64   5.737%   $265.0192   $265.02   $265.00   $265.00  
  Purchase #2 $102.84   4.597%   $107.5676   $107.57   $107.55   $107.60  
  Purchase #3 $87.67   7.424%   $94.1786   $94.18   $94.20   $94.20  
  Purchase #4 $162.68   11.639%   $181.6143   $181.61   $181.60   $181.60  
  Purchase #5 $39.97   12.368%   $44.9135   $44.91   $44.90   $44.90  
  Purchase #6 $246.62   8.709%   $268.0981   $268.10   $268.10   $268.10  
  Purchase #7 $8.91   10.360%   $9.8331   $9.83   $9.85   $9.80  
  7 purchase totals = $899.33       $971.2244   $971.22   $971.20   $971.20