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 $189.72   6.105%   $201.3024   $201.30   $201.30   $201.30  
  Purchase #2 $158.43   9.610%   $173.6551   $173.66   $173.65   $173.70  
  Purchase #3 $56.73   8.635%   $61.6286   $61.63   $61.65   $61.60  
  Purchase #4 $153.46   4.813%   $160.846   $160.85   $160.85   $160.80  
  Purchase #5 $207.53   7.142%   $222.3518   $222.35   $222.35   $222.40  
  Purchase #6 $182.32   11.667%   $203.5913   $203.59   $203.60   $203.60  
  Purchase #7 $41.85   9.151%   $45.6797   $45.68   $45.70   $45.70  
  7 purchase totals = $990.04       $1,069.0549   $1,069.06   $1,069.10   $1,069.10