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 $189.64   5.734%   $200.514   $200.51   $200.50   $200.50  
  Purchase #2 $22.37   5.155%   $23.5232   $23.52   $23.50   $23.50  
  Purchase #3 $227.64   4.714%   $238.3709   $238.37   $238.35   $238.40  
  Purchase #4 $168.99   4.507%   $176.6064   $176.61   $176.60   $176.60  
  Purchase #5 $197.26   11.614%   $220.1698   $220.17   $220.15   $220.20  
  Purchase #6 $243.53   10.865%   $269.9895   $269.99   $270.00   $270.00  
  Purchase #7 $234.75   4.202%   $244.6142   $244.61   $244.60   $244.60  
  7 purchase totals = $1,284.18       $1,373.7880   $1,373.78   $1,373.70   $1,373.80