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 $165.27   12.113%   $185.2892   $185.29   $185.30   $185.30  
  Purchase #2 $174.98   6.666%   $186.6442   $186.64   $186.65   $186.60  
  Purchase #3 $219.32   5.479%   $231.3365   $231.34   $231.35   $231.30  
  Purchase #4 $174.44   7.583%   $187.6678   $187.67   $187.65   $187.70  
  Purchase #5 $99.42   7.183%   $106.5613   $106.56   $106.55   $106.60  
  Purchase #6 $149.40   4.605%   $156.2799   $156.28   $156.30   $156.30  
  Purchase #7 $176.75   12.672%   $199.1478   $199.15   $199.15   $199.10  
  7 purchase totals = $1,159.58       $1,252.9267   $1,252.93   $1,252.95   $1,252.90