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 $244.54   9.315%   $267.3189   $267.32   $267.30   $267.30  
  Purchase #2 $196.70   9.633%   $215.6481   $215.65   $215.65   $215.60  
  Purchase #3 $80.77   10.141%   $88.9609   $88.96   $88.95   $89.00  
  Purchase #4 $85.34   8.835%   $92.8798   $92.88   $92.90   $92.90  
  Purchase #5 $136.26   7.590%   $146.6021   $146.60   $146.60   $146.60  
  Purchase #6 $193.67   3.164%   $199.7977   $199.80   $199.80   $199.80  
  Purchase #7 $215.71   4.479%   $225.3717   $225.37   $225.35   $225.40  
  7 purchase totals = $1,152.99       $1,236.5792   $1,236.58   $1,236.55   $1,236.60