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 $68.45   7.609%   $73.6584   $73.66   $73.65   $73.70  
  Purchase #2 $184.65   6.119%   $195.9487   $195.95   $195.95   $195.90  
  Purchase #3 $177.60   5.852%   $187.9932   $187.99   $188.00   $188.00  
  Purchase #4 $120.27   9.258%   $131.4046   $131.40   $131.40   $131.40  
  Purchase #5 $107.38   11.360%   $119.5784   $119.58   $119.60   $119.60  
  Purchase #6 $44.49   12.565%   $50.0802   $50.08   $50.10   $50.10  
  Purchase #7 $112.60   9.407%   $123.1923   $123.19   $123.20   $123.20  
  7 purchase totals = $815.44       $881.8558   $881.85   $881.90   $881.90