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 $78.95   10.658%   $87.3645   $87.36   $87.35   $87.40  
  Purchase #2 $103.88   9.405%   $113.6499   $113.65   $113.65   $113.60  
  Purchase #3 $145.39   9.155%   $158.7005   $158.70   $158.70   $158.70  
  Purchase #4 $51.40   6.129%   $54.5503   $54.55   $54.55   $54.60  
  Purchase #5 $134.85   13.673%   $153.288   $153.29   $153.30   $153.30  
  Purchase #6 $164.57   13.693%   $187.1046   $187.10   $187.10   $187.10  
  Purchase #7 $145.35   4.384%   $151.7221   $151.72   $151.70   $151.70  
  7 purchase totals = $824.39       $906.3799   $906.37   $906.35   $906.40