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 $73.28   6.261%   $77.8681   $77.87   $77.85   $77.90  
  Purchase #2 $101.30   7.418%   $108.8144   $108.81   $108.80   $108.80  
  Purchase #3 $109.50   10.841%   $121.3709   $121.37   $121.35   $121.40  
  Purchase #4 $78.76   3.847%   $81.7899   $81.79   $81.80   $81.80  
  Purchase #5 $141.26   9.807%   $155.1134   $155.11   $155.10   $155.10  
  Purchase #6 $86.39   4.615%   $90.3769   $90.38   $90.40   $90.40  
  Purchase #7 $181.53   7.517%   $195.1756   $195.18   $195.20   $195.20  
  7 purchase totals = $772.02       $830.5092   $830.51   $830.50   $830.60