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 $71.49   4.460%   $74.6785   $74.68   $74.70   $74.70  
  Purchase #2 $156.93   5.694%   $165.8656   $165.87   $165.85   $165.90  
  Purchase #3 $184.85   3.154%   $190.6802   $190.68   $190.70   $190.70  
  Purchase #4 $172.30   4.401%   $179.8829   $179.88   $179.90   $179.90  
  Purchase #5 $138.66   3.525%   $143.5478   $143.55   $143.55   $143.50  
  Purchase #6 $116.53   4.657%   $121.9568   $121.96   $121.95   $122.00  
  Purchase #7 $136.95   6.834%   $146.3092   $146.31   $146.30   $146.30  
  7 purchase totals = $977.71       $1,022.9210   $1,022.93   $1,022.95   $1,023.00