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 $56.58   8.344%   $61.301   $61.30   $61.30   $61.30  
  Purchase #2 $201.70   4.594%   $210.9661   $210.97   $210.95   $211.00  
  Purchase #3 $246.95   6.594%   $263.2339   $263.23   $263.25   $263.20  
  Purchase #4 $25.41   13.212%   $28.7672   $28.77   $28.75   $28.80  
  Purchase #5 $139.92   8.401%   $151.6747   $151.67   $151.65   $151.70  
  Purchase #6 $85.32   3.760%   $88.528   $88.53   $88.55   $88.50  
  Purchase #7 $90.47   6.146%   $96.0303   $96.03   $96.05   $96.00  
  7 purchase totals = $846.35       $900.5012   $900.50   $900.50   $900.50