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 $59.64   8.580%   $64.7571   $64.76   $64.75   $64.80  
  Purchase #2 $168.97   4.655%   $176.8356   $176.84   $176.85   $176.80  
  Purchase #3 $39.36   4.850%   $41.269   $41.27   $41.25   $41.30  
  Purchase #4 $22.33   9.350%   $24.4179   $24.42   $24.40   $24.40  
  Purchase #5 $237.82   6.251%   $252.6861   $252.69   $252.70   $252.70  
  Purchase #6 $46.73   10.657%   $51.71   $51.71   $51.70   $51.70  
  Purchase #7 $117.45   6.173%   $124.7002   $124.70   $124.70   $124.70  
  7 purchase totals = $692.30       $736.3759   $736.39   $736.35   $736.40