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 $201.32   11.766%   $225.0073   $225.01   $225.00   $225.00  
  Purchase #2 $174.91   13.113%   $197.8459   $197.85   $197.85   $197.80  
  Purchase #3 $75.43   8.331%   $81.7141   $81.71   $81.70   $81.70  
  Purchase #4 $230.85   11.830%   $258.1596   $258.16   $258.15   $258.20  
  Purchase #5 $152.74   11.511%   $170.3219   $170.32   $170.30   $170.30  
  Purchase #6 $55.96   10.535%   $61.8554   $61.86   $61.85   $61.90  
  Purchase #7 $73.97   13.635%   $84.0558   $84.06   $84.05   $84.10  
  7 purchase totals = $965.18       $1,078.9600   $1,078.97   $1,078.90   $1,079.00