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 $45.96   3.523%   $47.5792   $47.58   $47.60   $47.60  
  Purchase #2 $248.86   5.407%   $262.3159   $262.32   $262.30   $262.30  
  Purchase #3 $104.64   4.107%   $108.9376   $108.94   $108.95   $108.90  
  Purchase #4 $181.93   12.397%   $204.4839   $204.48   $204.50   $204.50  
  Purchase #5 $131.75   9.532%   $144.3084   $144.31   $144.30   $144.30  
  Purchase #6 $45.93   13.649%   $52.199   $52.20   $52.20   $52.20  
  Purchase #7 $134.57   5.217%   $141.5905   $141.59   $141.60   $141.60  
  7 purchase totals = $893.64       $961.4145   $961.42   $961.45   $961.40