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 $198.56   13.621%   $225.6059   $225.61   $225.60   $225.60  
  Purchase #2 $168.92   7.517%   $181.6177   $181.62   $181.60   $181.60  
  Purchase #3 $124.46   13.605%   $141.3928   $141.39   $141.40   $141.40  
  Purchase #4 $220.74   10.451%   $243.8095   $243.81   $243.80   $243.80  
  Purchase #5 $132.50   5.411%   $139.6696   $139.67   $139.65   $139.70  
  Purchase #6 $247.28   7.760%   $266.4689   $266.47   $266.45   $266.50  
  Purchase #7 $30.29   12.313%   $34.0196   $34.02   $34.00   $34.00  
  7 purchase totals = $1,122.75       $1,232.5840   $1,232.59   $1,232.50   $1,232.60