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 $61.37   8.671%   $66.6914   $66.69   $66.70   $66.70  
  Purchase #2 $204.31   6.667%   $217.9313   $217.93   $217.95   $217.90  
  Purchase #3 $26.77   4.400%   $27.9479   $27.95   $27.95   $27.90  
  Purchase #4 $125.31   7.184%   $134.3123   $134.31   $134.30   $134.30  
  Purchase #5 $218.47   9.322%   $238.8358   $238.84   $238.85   $238.80  
  Purchase #6 $23.89   11.425%   $26.6194   $26.62   $26.60   $26.60  
  Purchase #7 $195.64   12.237%   $219.5805   $219.58   $219.60   $219.60  
  7 purchase totals = $855.76       $931.9186   $931.92   $931.95   $931.80