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 $53.86   12.405%   $60.5413   $60.54   $60.55   $60.50  
  Purchase #2 $5.48   13.382%   $6.2133   $6.21   $6.20   $6.20  
  Purchase #3 $149.29   13.447%   $169.365   $169.37   $169.35   $169.40  
  Purchase #4 $237.43   13.384%   $269.2076   $269.21   $269.20   $269.20  
  Purchase #5 $199.36   7.199%   $213.7119   $213.71   $213.70   $213.70  
  Purchase #6 $221.37   7.407%   $237.7669   $237.77   $237.75   $237.80  
  Purchase #7 $180.50   13.813%   $205.4325   $205.43   $205.45   $205.40  
  7 purchase totals = $1,047.29       $1,162.2385   $1,162.24   $1,162.20   $1,162.20