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 $38.52   12.643%   $43.3901   $43.39   $43.40   $43.40  
  Purchase #2 $159.35   13.483%   $180.8352   $180.84   $180.85   $180.80  
  Purchase #3 $207.67   6.634%   $221.4468   $221.45   $221.45   $221.40  
  Purchase #4 $225.50   6.810%   $240.8566   $240.86   $240.85   $240.90  
  Purchase #5 $34.49   10.783%   $38.2091   $38.21   $38.20   $38.20  
  Purchase #6 $143.46   9.815%   $157.5406   $157.54   $157.55   $157.50  
  Purchase #7 $171.85   3.583%   $178.0074   $178.01   $178.00   $178.00  
  7 purchase totals = $980.84       $1,060.2858   $1,060.30   $1,060.30   $1,060.20