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 $181.54   4.486%   $189.6839   $189.68   $189.70   $189.70  
  Purchase #2 $94.99   12.288%   $106.6624   $106.66   $106.65   $106.70  
  Purchase #3 $91.92   5.511%   $96.9857   $96.99   $97.00   $97.00  
  Purchase #4 $125.61   4.199%   $130.8844   $130.88   $130.90   $130.90  
  Purchase #5 $207.61   3.249%   $214.3552   $214.36   $214.35   $214.40  
  Purchase #6 $246.64   6.471%   $262.6001   $262.60   $262.60   $262.60  
  Purchase #7 $140.74   7.740%   $151.6333   $151.63   $151.65   $151.60  
  7 purchase totals = $1,089.05       $1,152.8050   $1,152.80   $1,152.85   $1,152.90