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 $22.86   8.327%   $24.7636   $24.76   $24.75   $24.80  
  Purchase #2 $175.46   12.459%   $197.3206   $197.32   $197.30   $197.30  
  Purchase #3 $124.40   3.372%   $128.5948   $128.59   $128.60   $128.60  
  Purchase #4 $84.46   12.168%   $94.7371   $94.74   $94.75   $94.70  
  Purchase #5 $160.73   13.163%   $181.8869   $181.89   $181.90   $181.90  
  Purchase #6 $88.58   9.318%   $96.8339   $96.83   $96.85   $96.80  
  Purchase #7 $240.49   6.711%   $256.6293   $256.63   $256.65   $256.60  
  7 purchase totals = $896.98       $980.7662   $980.76   $980.80   $980.70