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 $96.77   5.528%   $102.1194   $102.12   $102.10   $102.10  
  Purchase #2 $123.95   10.583%   $137.0676   $137.07   $137.05   $137.10  
  Purchase #3 $10.88   6.407%   $11.5771   $11.58   $11.60   $11.60  
  Purchase #4 $233.45   13.484%   $264.9284   $264.93   $264.95   $264.90  
  Purchase #5 $44.67   12.120%   $50.084   $50.08   $50.10   $50.10  
  Purchase #6 $203.93   3.477%   $211.0206   $211.02   $211.00   $211.00  
  Purchase #7 $213.28   9.429%   $233.3902   $233.39   $233.40   $233.40  
  7 purchase totals = $926.93       $1,010.1873   $1,010.19   $1,010.20   $1,010.20