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 $225.84   7.692%   $243.2116   $243.21   $243.20   $243.20  
  Purchase #2 $209.37   9.665%   $229.6056   $229.61   $229.60   $229.60  
  Purchase #3 $105.45   13.755%   $119.9546   $119.95   $119.95   $120.00  
  Purchase #4 $234.48   13.653%   $266.4936   $266.49   $266.50   $266.50  
  Purchase #5 $69.57   7.168%   $74.5568   $74.56   $74.55   $74.60  
  Purchase #6 $139.48   6.539%   $148.6006   $148.60   $148.60   $148.60  
  Purchase #7 $75.89   10.311%   $83.715   $83.72   $83.70   $83.70  
  7 purchase totals = $1,060.08       $1,166.1378   $1,166.14   $1,166.10   $1,166.20