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 $98.85   10.869%   $109.594   $109.59   $109.60   $109.60  
  Purchase #2 $42.56   6.110%   $45.1604   $45.16   $45.15   $45.20  
  Purchase #3 $54.77   6.115%   $58.1192   $58.12   $58.10   $58.10  
  Purchase #4 $244.44   7.840%   $263.6041   $263.60   $263.60   $263.60  
  Purchase #5 $119.50   4.835%   $125.2778   $125.28   $125.30   $125.30  
  Purchase #6 $120.84   11.833%   $135.139   $135.14   $135.15   $135.10  
  Purchase #7 $154.46   5.384%   $162.7761   $162.78   $162.80   $162.80  
  7 purchase totals = $835.42       $899.6706   $899.67   $899.70   $899.70