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 $142.86   8.638%   $155.2002   $155.20   $155.20   $155.20  
  Purchase #2 $113.58   5.343%   $119.6486   $119.65   $119.65   $119.60  
  Purchase #3 $184.88   3.779%   $191.8666   $191.87   $191.85   $191.90  
  Purchase #4 $113.28   9.739%   $124.3123   $124.31   $124.30   $124.30  
  Purchase #5 $67.75   12.539%   $76.2452   $76.25   $76.25   $76.20  
  Purchase #6 $203.37   12.512%   $228.8157   $228.82   $228.80   $228.80  
  Purchase #7 $173.45   9.137%   $189.2981   $189.30   $189.30   $189.30  
  7 purchase totals = $999.17       $1,085.3867   $1,085.40   $1,085.35   $1,085.30