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 $207.75   8.298%   $224.9891   $224.99   $225.00   $225.00  
  Purchase #2 $59.72   3.604%   $61.8723   $61.87   $61.85   $61.90  
  Purchase #3 $220.42   3.646%   $228.4565   $228.46   $228.45   $228.50  
  Purchase #4 $77.92   3.411%   $80.5779   $80.58   $80.60   $80.60  
  Purchase #5 $230.26   12.123%   $258.1744   $258.17   $258.15   $258.20  
  Purchase #6 $218.78   6.560%   $233.132   $233.13   $233.15   $233.10  
  Purchase #7 $149.28   11.682%   $166.7189   $166.72   $166.70   $166.70  
  7 purchase totals = $1,164.13       $1,253.9211   $1,253.92   $1,253.90   $1,254.00