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 $208.52   8.158%   $225.5311   $225.53   $225.55   $225.50  
  Purchase #2 $59.91   9.107%   $65.366   $65.37   $65.35   $65.40  
  Purchase #3 $143.48   11.259%   $159.6344   $159.63   $159.65   $159.60  
  Purchase #4 $143.70   7.160%   $153.9889   $153.99   $154.00   $154.00  
  Purchase #5 $167.80   10.817%   $185.9509   $185.95   $185.95   $186.00  
  Purchase #6 $178.95   5.525%   $188.837   $188.84   $188.85   $188.80  
  Purchase #7 $142.96   5.607%   $150.9758   $150.98   $151.00   $151.00  
  7 purchase totals = $1,045.32       $1,130.2841   $1,130.29   $1,130.35   $1,130.30