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 $78.43   8.428%   $85.0401   $85.04   $85.05   $85.00  
  Purchase #2 $170.53   7.402%   $183.1526   $183.15   $183.15   $183.20  
  Purchase #3 $200.44   12.538%   $225.5712   $225.57   $225.55   $225.60  
  Purchase #4 $8.46   12.635%   $9.5289   $9.53   $9.55   $9.50  
  Purchase #5 $225.63   4.199%   $235.1042   $235.10   $235.10   $235.10  
  Purchase #6 $110.65   12.697%   $124.6992   $124.70   $124.70   $124.70  
  Purchase #7 $200.51   4.362%   $209.2562   $209.26   $209.25   $209.30  
  7 purchase totals = $994.65       $1,072.3524   $1,072.35   $1,072.35   $1,072.40