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 $197.86   11.559%   $220.7306   $220.73   $220.75   $220.70  
  Purchase #2 $219.58   6.371%   $233.5694   $233.57   $233.55   $233.60  
  Purchase #3 $96.65   6.345%   $102.7824   $102.78   $102.80   $102.80  
  Purchase #4 $17.33   12.235%   $19.4503   $19.45   $19.45   $19.50  
  Purchase #5 $201.58   12.165%   $226.1022   $226.10   $226.10   $226.10  
  Purchase #6 $204.37   8.661%   $222.0705   $222.07   $222.05   $222.10  
  Purchase #7 $31.87   8.870%   $34.6969   $34.70   $34.70   $34.70  
  7 purchase totals = $969.24       $1,059.4023   $1,059.40   $1,059.40   $1,059.50