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 $87.58   8.278%   $94.8299   $94.83   $94.85   $94.80  
  Purchase #2 $242.28   11.755%   $270.76   $270.76   $270.75   $270.80  
  Purchase #3 $28.55   10.164%   $31.4518   $31.45   $31.45   $31.50  
  Purchase #4 $147.49   12.589%   $166.0575   $166.06   $166.05   $166.10  
  Purchase #5 $179.62   10.607%   $198.6723   $198.67   $198.65   $198.70  
  Purchase #6 $80.57   7.531%   $86.6377   $86.64   $86.65   $86.60  
  Purchase #7 $166.73   11.634%   $186.1274   $186.13   $186.15   $186.10  
  7 purchase totals = $932.82       $1,034.5366   $1,034.54   $1,034.55   $1,034.60