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 $146.84   13.790%   $167.0892   $167.09   $167.10   $167.10  
  Purchase #2 $173.84   4.494%   $181.6524   $181.65   $181.65   $181.70  
  Purchase #3 $153.95   11.351%   $171.4249   $171.42   $171.40   $171.40  
  Purchase #4 $204.66   6.490%   $217.9424   $217.94   $217.95   $217.90  
  Purchase #5 $87.30   6.874%   $93.301   $93.30   $93.30   $93.30  
  Purchase #6 $164.44   5.607%   $173.6602   $173.66   $173.65   $173.70  
  Purchase #7 $236.40   12.739%   $266.515   $266.52   $266.50   $266.50  
  7 purchase totals = $1,167.43       $1,271.5851   $1,271.58   $1,271.55   $1,271.60