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 $21.39   4.136%   $22.2747   $22.27   $22.25   $22.30  
  Purchase #2 $237.26   11.299%   $264.068   $264.07   $264.05   $264.10  
  Purchase #3 $137.35   3.280%   $141.8551   $141.86   $141.85   $141.90  
  Purchase #4 $224.94   11.500%   $250.8081   $250.81   $250.80   $250.80  
  Purchase #5 $215.36   8.774%   $234.2557   $234.26   $234.25   $234.30  
  Purchase #6 $91.45   9.390%   $100.0372   $100.04   $100.05   $100.00  
  Purchase #7 $138.67   6.294%   $147.3979   $147.40   $147.40   $147.40  
  7 purchase totals = $1,066.42       $1,160.6967   $1,160.71   $1,160.65   $1,160.80