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 $46.34   6.103%   $49.1681   $49.17   $49.15   $49.20  
  Purchase #2 $212.72   10.862%   $235.8256   $235.83   $235.85   $235.80  
  Purchase #3 $200.75   12.544%   $225.9321   $225.93   $225.95   $225.90  
  Purchase #4 $59.53   10.360%   $65.6973   $65.70   $65.70   $65.70  
  Purchase #5 $78.85   6.559%   $84.0218   $84.02   $84.00   $84.00  
  Purchase #6 $24.82   6.648%   $26.47   $26.47   $26.45   $26.50  
  Purchase #7 $14.59   6.139%   $15.4857   $15.49   $15.50   $15.50  
  7 purchase totals = $637.60       $702.6006   $702.61   $702.60   $702.60