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 $166.37   10.147%   $183.2516   $183.25   $183.25   $183.30  
  Purchase #2 $217.44   10.664%   $240.6278   $240.63   $240.65   $240.60  
  Purchase #3 $218.63   7.656%   $235.3683   $235.37   $235.35   $235.40  
  Purchase #4 $145.39   7.684%   $156.5618   $156.56   $156.55   $156.60  
  Purchase #5 $90.57   6.290%   $96.2669   $96.27   $96.25   $96.30  
  Purchase #6 $184.30   6.826%   $196.8803   $196.88   $196.90   $196.90  
  Purchase #7 $228.87   6.430%   $243.5863   $243.59   $243.60   $243.60  
  7 purchase totals = $1,251.57       $1,352.5430   $1,352.55   $1,352.55   $1,352.70