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 $227.58   10.463%   $251.3917   $251.39   $251.40   $251.40  
  Purchase #2 $183.57   8.164%   $198.5567   $198.56   $198.55   $198.60  
  Purchase #3 $189.95   3.775%   $197.1206   $197.12   $197.10   $197.10  
  Purchase #4 $63.61   9.308%   $69.5308   $69.53   $69.55   $69.50  
  Purchase #5 $122.47   9.343%   $133.9124   $133.91   $133.90   $133.90  
  Purchase #6 $43.57   11.298%   $48.4925   $48.49   $48.50   $48.50  
  Purchase #7 $165.84   7.352%   $178.0326   $178.03   $178.05   $178.00  
  7 purchase totals = $996.59       $1,077.0373   $1,077.03   $1,077.05   $1,077.00