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 $118.86   4.636%   $124.3703   $124.37   $124.35   $124.40  
  Purchase #2 $208.49   3.853%   $216.5231   $216.52   $216.50   $216.50  
  Purchase #3 $99.46   3.662%   $103.1022   $103.10   $103.10   $103.10  
  Purchase #4 $130.43   3.274%   $134.7003   $134.70   $134.70   $134.70  
  Purchase #5 $111.89   12.565%   $125.949   $125.95   $125.95   $125.90  
  Purchase #6 $204.33   7.860%   $220.3903   $220.39   $220.40   $220.40  
  Purchase #7 $77.98   12.799%   $87.9607   $87.96   $87.95   $88.00  
  7 purchase totals = $951.44       $1,012.9959   $1,012.99   $1,012.95   $1,013.00