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 $89.53   5.229%   $94.2115   $94.21   $94.20   $94.20  
  Purchase #2 $169.51   7.254%   $181.8063   $181.81   $181.80   $181.80  
  Purchase #3 $178.64   6.137%   $189.6031   $189.60   $189.60   $189.60  
  Purchase #4 $11.48   5.479%   $12.109   $12.11   $12.10   $12.10  
  Purchase #5 $98.35   4.247%   $102.5269   $102.53   $102.55   $102.50  
  Purchase #6 $14.29   7.797%   $15.4042   $15.40   $15.40   $15.40  
  Purchase #7 $249.46   6.374%   $265.3606   $265.36   $265.35   $265.40  
  7 purchase totals = $811.26       $861.0216   $861.02   $861.00   $861.00