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 $71.71   5.418%   $75.5952   $75.60   $75.60   $75.60  
  Purchase #2 $31.52   9.796%   $34.6077   $34.61   $34.60   $34.60  
  Purchase #3 $213.48   10.527%   $235.953   $235.95   $235.95   $236.00  
  Purchase #4 $37.84   4.484%   $39.5367   $39.54   $39.55   $39.50  
  Purchase #5 $106.25   5.280%   $111.86   $111.86   $111.85   $111.90  
  Purchase #6 $144.68   12.311%   $162.4916   $162.49   $162.50   $162.50  
  Purchase #7 $238.30   12.448%   $267.9636   $267.96   $267.95   $268.00  
  7 purchase totals = $843.78       $928.0078   $928.01   $928.00   $928.10