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 $62.33   10.121%   $68.6384   $68.64   $68.65   $68.60  
  Purchase #2 $206.82   13.169%   $234.0561   $234.06   $234.05   $234.10  
  Purchase #3 $226.82   7.516%   $243.8678   $243.87   $243.85   $243.90  
  Purchase #4 $195.84   8.312%   $212.1182   $212.12   $212.10   $212.10  
  Purchase #5 $192.49   6.103%   $204.2377   $204.24   $204.25   $204.20  
  Purchase #6 $231.73   5.595%   $244.6953   $244.70   $244.70   $244.70  
  Purchase #7 $153.46   9.692%   $168.3333   $168.33   $168.35   $168.30  
  7 purchase totals = $1,269.49       $1,375.9468   $1,375.96   $1,375.95   $1,375.90