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 $137.29   13.229%   $155.4521   $155.45   $155.45   $155.50  
  Purchase #2 $246.98   7.533%   $265.585   $265.59   $265.60   $265.60  
  Purchase #3 $22.65   3.848%   $23.5216   $23.52   $23.50   $23.50  
  Purchase #4 $28.26   9.767%   $31.0202   $31.02   $31.00   $31.00  
  Purchase #5 $243.97   9.683%   $267.5936   $267.59   $267.60   $267.60  
  Purchase #6 $113.65   11.764%   $127.0198   $127.02   $127.00   $127.00  
  Purchase #7 $158.73   4.520%   $165.9046   $165.90   $165.90   $165.90  
  7 purchase totals = $951.53       $1,036.0969   $1,036.09   $1,036.05   $1,036.10