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 $240.97   9.803%   $264.5923   $264.59   $264.60   $264.60  
  Purchase #2 $204.36   13.162%   $231.2579   $231.26   $231.25   $231.30  
  Purchase #3 $155.34   13.635%   $176.5206   $176.52   $176.50   $176.50  
  Purchase #4 $246.71   12.386%   $277.2675   $277.27   $277.25   $277.30  
  Purchase #5 $139.31   10.456%   $153.8763   $153.88   $153.90   $153.90  
  Purchase #6 $88.80   12.170%   $99.607   $99.61   $99.60   $99.60  
  Purchase #7 $233.45   6.275%   $248.099   $248.10   $248.10   $248.10  
  7 purchase totals = $1,308.94       $1,451.2206   $1,451.23   $1,451.20   $1,451.30