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 $102.94   3.232%   $106.267   $106.27   $106.25   $106.30  
  Purchase #2 $43.96   6.401%   $46.7739   $46.77   $46.75   $46.80  
  Purchase #3 $210.66   4.331%   $219.7837   $219.78   $219.80   $219.80  
  Purchase #4 $118.84   3.170%   $122.6072   $122.61   $122.60   $122.60  
  Purchase #5 $113.85   9.340%   $124.4836   $124.48   $124.50   $124.50  
  Purchase #6 $129.66   3.351%   $134.0049   $134.00   $134.00   $134.00  
  Purchase #7 $198.82   3.365%   $205.5103   $205.51   $205.50   $205.50  
  7 purchase totals = $918.73       $959.4306   $959.42   $959.40   $959.50