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 $76.81   10.609%   $84.9588   $84.96   $84.95   $85.00  
  Purchase #2 $71.98   13.441%   $81.6548   $81.65   $81.65   $81.70  
  Purchase #3 $155.31   12.629%   $174.9241   $174.92   $174.90   $174.90  
  Purchase #4 $59.87   7.546%   $64.3878   $64.39   $64.40   $64.40  
  Purchase #5 $139.28   5.823%   $147.3903   $147.39   $147.40   $147.40  
  Purchase #6 $117.26   9.241%   $128.096   $128.10   $128.10   $128.10  
  Purchase #7 $91.98   7.220%   $98.621   $98.62   $98.60   $98.60  
  7 purchase totals = $712.49       $780.0328   $780.03   $780.00   $780.10