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 $178.75   11.516%   $199.3349   $199.33   $199.35   $199.30  
  Purchase #2 $156.77   7.549%   $168.6046   $168.60   $168.60   $168.60  
  Purchase #3 $118.58   13.585%   $134.6891   $134.69   $134.70   $134.70  
  Purchase #4 $228.72   6.620%   $243.8613   $243.86   $243.85   $243.90  
  Purchase #5 $55.83   11.112%   $62.0338   $62.03   $62.05   $62.00  
  Purchase #6 $238.70   6.833%   $255.0104   $255.01   $255.00   $255.00  
  Purchase #7 $220.73   5.606%   $233.1041   $233.10   $233.10   $233.10  
  7 purchase totals = $1,198.08       $1,296.6382   $1,296.62   $1,296.65   $1,296.60