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 $209.90   6.479%   $223.4994   $223.50   $223.50   $223.50  
  Purchase #2 $37.40   3.127%   $38.5695   $38.57   $38.55   $38.60  
  Purchase #3 $62.68   9.415%   $68.5813   $68.58   $68.60   $68.60  
  Purchase #4 $177.52   3.549%   $183.8202   $183.82   $183.80   $183.80  
  Purchase #5 $69.33   7.310%   $74.398   $74.40   $74.40   $74.40  
  Purchase #6 $236.45   8.508%   $256.5672   $256.57   $256.55   $256.60  
  Purchase #7 $193.35   11.225%   $215.0535   $215.05   $215.05   $215.10  
  7 purchase totals = $986.63       $1,060.4891   $1,060.49   $1,060.45   $1,060.60