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 $194.46   10.631%   $215.133   $215.13   $215.15   $215.10  
  Purchase #2 $243.99   13.352%   $276.5675   $276.57   $276.55   $276.60  
  Purchase #3 $120.56   13.247%   $136.5306   $136.53   $136.55   $136.50  
  Purchase #4 $153.65   10.261%   $169.416   $169.42   $169.40   $169.40  
  Purchase #5 $233.34   9.765%   $256.1257   $256.13   $256.15   $256.10  
  Purchase #6 $181.44   13.666%   $206.2356   $206.24   $206.25   $206.20  
  Purchase #7 $227.33   8.207%   $245.987   $245.99   $246.00   $246.00  
  7 purchase totals = $1,354.77       $1,505.9954   $1,506.01   $1,506.05   $1,505.90