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 $38.65   7.764%   $41.6508   $41.65   $41.65   $41.70  
  Purchase #2 $241.67   7.610%   $260.0611   $260.06   $260.05   $260.10  
  Purchase #3 $117.38   4.640%   $122.8264   $122.83   $122.85   $122.80  
  Purchase #4 $55.46   8.175%   $59.9939   $59.99   $60.00   $60.00  
  Purchase #5 $186.55   4.229%   $194.4392   $194.44   $194.45   $194.40  
  Purchase #6 $5.98   4.402%   $6.2432   $6.24   $6.25   $6.20  
  Purchase #7 $24.89   9.829%   $27.3364   $27.34   $27.35   $27.30  
  7 purchase totals = $670.58       $712.5510   $712.55   $712.60   $712.50