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 $192.98   9.261%   $210.8519   $210.85   $210.85   $210.90  
  Purchase #2 $96.26   8.650%   $104.5865   $104.59   $104.60   $104.60  
  Purchase #3 $221.49   8.475%   $240.2613   $240.26   $240.25   $240.30  
  Purchase #4 $53.97   4.243%   $56.2599   $56.26   $56.25   $56.30  
  Purchase #5 $235.63   12.675%   $265.4961   $265.50   $265.50   $265.50  
  Purchase #6 $202.70   7.835%   $218.5815   $218.58   $218.60   $218.60  
  Purchase #7 $228.38   7.840%   $246.285   $246.29   $246.30   $246.30  
  7 purchase totals = $1,231.41       $1,342.3222   $1,342.33   $1,342.35   $1,342.50