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 $34.38   8.273%   $37.2243   $37.22   $37.20   $37.20  
  Purchase #2 $34.46   10.329%   $38.0194   $38.02   $38.00   $38.00  
  Purchase #3 $207.71   5.413%   $218.9533   $218.95   $218.95   $219.00  
  Purchase #4 $32.76   8.213%   $35.4506   $35.45   $35.45   $35.50  
  Purchase #5 $247.76   10.696%   $274.2604   $274.26   $274.25   $274.30  
  Purchase #6 $69.32   5.788%   $73.3322   $73.33   $73.35   $73.30  
  Purchase #7 $24.33   5.179%   $25.5901   $25.59   $25.60   $25.60  
  7 purchase totals = $650.72       $702.8303   $702.82   $702.80   $702.90