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 $66.67   3.713%   $69.1455   $69.15   $69.15   $69.10  
  Purchase #2 $201.41   4.538%   $210.55   $210.55   $210.55   $210.60  
  Purchase #3 $159.52   10.185%   $175.7671   $175.77   $175.75   $175.80  
  Purchase #4 $211.92   13.844%   $241.2582   $241.26   $241.25   $241.30  
  Purchase #5 $236.70   7.223%   $253.7968   $253.80   $253.80   $253.80  
  Purchase #6 $25.98   7.272%   $27.8693   $27.87   $27.85   $27.90  
  Purchase #7 $209.31   10.535%   $231.3608   $231.36   $231.35   $231.40  
  7 purchase totals = $1,111.51       $1,209.7477   $1,209.76   $1,209.70   $1,209.90