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 $202.59   10.822%   $224.5143   $224.51   $224.50   $224.50  
  Purchase #2 $240.91   11.806%   $269.3518   $269.35   $269.35   $269.40  
  Purchase #3 $95.33   11.803%   $106.5818   $106.58   $106.60   $106.60  
  Purchase #4 $162.51   9.120%   $177.3309   $177.33   $177.35   $177.30  
  Purchase #5 $121.42   12.368%   $136.4372   $136.44   $136.45   $136.40  
  Purchase #6 $13.93   5.635%   $14.715   $14.72   $14.70   $14.70  
  Purchase #7 $242.36   9.542%   $265.486   $265.49   $265.50   $265.50  
  7 purchase totals = $1,079.05       $1,194.4170   $1,194.42   $1,194.45   $1,194.40