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 $113.32   8.575%   $123.0372   $123.04   $123.05   $123.00  
  Purchase #2 $152.86   11.758%   $170.8333   $170.83   $170.85   $170.80  
  Purchase #3 $69.68   8.722%   $75.7575   $75.76   $75.75   $75.80  
  Purchase #4 $187.57   8.113%   $202.7876   $202.79   $202.80   $202.80  
  Purchase #5 $27.84   7.157%   $29.8325   $29.83   $29.85   $29.80  
  Purchase #6 $208.44   8.173%   $225.4758   $225.48   $225.50   $225.50  
  Purchase #7 $113.56   3.156%   $117.144   $117.14   $117.15   $117.10  
  7 purchase totals = $873.27       $944.8679   $944.87   $944.95   $944.80