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 $247.42   8.664%   $268.8565   $268.86   $268.85   $268.90  
  Purchase #2 $136.69   4.425%   $142.7385   $142.74   $142.75   $142.70  
  Purchase #3 $9.74   4.813%   $10.2088   $10.21   $10.20   $10.20  
  Purchase #4 $161.95   12.164%   $181.6496   $181.65   $181.65   $181.60  
  Purchase #5 $179.49   9.844%   $197.159   $197.16   $197.15   $197.20  
  Purchase #6 $210.79   5.869%   $223.1613   $223.16   $223.15   $223.20  
  Purchase #7 $136.97   9.458%   $149.9246   $149.92   $149.90   $149.90  
  7 purchase totals = $1,083.05       $1,173.6983   $1,173.70   $1,173.65   $1,173.70