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 $60.58   13.683%   $68.8692   $68.87   $68.85   $68.90  
  Purchase #2 $59.53   6.458%   $63.3744   $63.37   $63.35   $63.40  
  Purchase #3 $54.61   3.479%   $56.5099   $56.51   $56.50   $56.50  
  Purchase #4 $91.36   11.577%   $101.9367   $101.94   $101.95   $101.90  
  Purchase #5 $41.26   11.438%   $45.9793   $45.98   $46.00   $46.00  
  Purchase #6 $179.35   12.578%   $201.9086   $201.91   $201.90   $201.90  
  Purchase #7 $170.59   10.152%   $187.9083   $187.91   $187.90   $187.90  
  7 purchase totals = $657.28       $726.4864   $726.49   $726.45   $726.50