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 $84.59   9.444%   $92.5787   $92.58   $92.60   $92.60  
  Purchase #2 $202.50   12.540%   $227.8935   $227.89   $227.90   $227.90  
  Purchase #3 $170.99   6.410%   $181.9505   $181.95   $181.95   $182.00  
  Purchase #4 $206.88   7.317%   $222.0174   $222.02   $222.00   $222.00  
  Purchase #5 $100.83   11.698%   $112.6251   $112.63   $112.65   $112.60  
  Purchase #6 $71.53   3.485%   $74.0228   $74.02   $74.00   $74.00  
  Purchase #7 $151.85   9.622%   $166.461   $166.46   $166.45   $166.50  
  7 purchase totals = $989.17       $1,077.5490   $1,077.55   $1,077.55   $1,077.60