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 $172.95   13.461%   $196.2308   $196.23   $196.25   $196.20  
  Purchase #2 $76.96   6.522%   $81.9793   $81.98   $82.00   $82.00  
  Purchase #3 $31.95   3.798%   $33.1635   $33.16   $33.15   $33.20  
  Purchase #4 $75.29   5.709%   $79.5883   $79.59   $79.60   $79.60  
  Purchase #5 $185.94   13.159%   $210.4078   $210.41   $210.40   $210.40  
  Purchase #6 $112.35   9.155%   $122.6356   $122.64   $122.65   $122.60  
  Purchase #7 $202.67   13.263%   $229.5501   $229.55   $229.55   $229.60  
  7 purchase totals = $858.11       $953.5554   $953.56   $953.60   $953.60