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 $22.79   6.153%   $24.1923   $24.19   $24.20   $24.20  
  Purchase #2 $181.49   13.861%   $206.6463   $206.65   $206.65   $206.60  
  Purchase #3 $48.44   6.762%   $51.7155   $51.72   $51.70   $51.70  
  Purchase #4 $149.80   10.577%   $165.6443   $165.64   $165.65   $165.60  
  Purchase #5 $242.62   9.356%   $265.3195   $265.32   $265.30   $265.30  
  Purchase #6 $201.85   13.843%   $229.7921   $229.79   $229.80   $229.80  
  Purchase #7 $235.42   3.231%   $243.0264   $243.03   $243.05   $243.00  
  7 purchase totals = $1,082.41       $1,186.3364   $1,186.34   $1,186.35   $1,186.20