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 $9.55   10.567%   $10.5591   $10.56   $10.55   $10.60  
  Purchase #2 $48.53   7.751%   $52.2916   $52.29   $52.30   $52.30  
  Purchase #3 $61.56   6.791%   $65.7405   $65.74   $65.75   $65.70  
  Purchase #4 $127.58   4.125%   $132.8427   $132.84   $132.85   $132.80  
  Purchase #5 $74.80   13.194%   $84.6691   $84.67   $84.65   $84.70  
  Purchase #6 $235.66   12.597%   $265.3461   $265.35   $265.35   $265.30  
  Purchase #7 $120.63   11.510%   $134.5145   $134.51   $134.50   $134.50  
  7 purchase totals = $678.31       $745.9636   $745.96   $745.95   $745.90