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 $24.79   11.470%   $27.6334   $27.63   $27.65   $27.60  
  Purchase #2 $95.83   10.725%   $106.1078   $106.11   $106.10   $106.10  
  Purchase #3 $218.74   12.711%   $246.544   $246.54   $246.55   $246.50  
  Purchase #4 $193.36   7.300%   $207.4753   $207.48   $207.50   $207.50  
  Purchase #5 $46.33   5.735%   $48.987   $48.99   $49.00   $49.00  
  Purchase #6 $223.72   6.467%   $238.188   $238.19   $238.20   $238.20  
  Purchase #7 $134.26   3.216%   $138.5778   $138.58   $138.60   $138.60  
  7 purchase totals = $937.03       $1,013.5133   $1,013.52   $1,013.60   $1,013.50