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 $65.37   12.116%   $73.2902   $73.29   $73.30   $73.30  
  Purchase #2 $211.82   4.435%   $221.2142   $221.21   $221.20   $221.20  
  Purchase #3 $152.42   13.102%   $172.3901   $172.39   $172.40   $172.40  
  Purchase #4 $156.66   11.530%   $174.7229   $174.72   $174.70   $174.70  
  Purchase #5 $10.91   5.813%   $11.5442   $11.54   $11.55   $11.50  
  Purchase #6 $83.54   4.637%   $87.4137   $87.41   $87.40   $87.40  
  Purchase #7 $29.39   5.741%   $31.0773   $31.08   $31.10   $31.10  
  7 purchase totals = $710.11       $771.6526   $771.64   $771.65   $771.60