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 $106.36   8.628%   $115.5367   $115.54   $115.55   $115.50  
  Purchase #2 $238.84   11.435%   $266.1514   $266.15   $266.15   $266.20  
  Purchase #3 $43.26   5.216%   $45.5164   $45.52   $45.50   $45.50  
  Purchase #4 $93.70   10.764%   $103.7859   $103.79   $103.80   $103.80  
  Purchase #5 $30.97   6.487%   $32.979   $32.98   $33.00   $33.00  
  Purchase #6 $240.30   7.673%   $258.7382   $258.74   $258.75   $258.70  
  Purchase #7 $142.73   7.735%   $153.7702   $153.77   $153.75   $153.80  
  7 purchase totals = $896.16       $976.4778   $976.49   $976.50   $976.50