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 $58.53   12.502%   $65.8474   $65.85   $65.85   $65.80  
  Purchase #2 $243.25   7.805%   $262.2357   $262.24   $262.25   $262.20  
  Purchase #3 $35.99   8.864%   $39.1802   $39.18   $39.20   $39.20  
  Purchase #4 $218.31   5.333%   $229.9525   $229.95   $229.95   $230.00  
  Purchase #5 $99.46   7.273%   $106.6937   $106.69   $106.70   $106.70  
  Purchase #6 $233.25   9.761%   $256.0175   $256.02   $256.00   $256.00  
  Purchase #7 $51.87   3.341%   $53.603   $53.60   $53.60   $53.60  
  7 purchase totals = $940.66       $1,013.5300   $1,013.53   $1,013.55   $1,013.50