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 $154.97   7.486%   $166.5711   $166.57   $166.55   $166.60  
  Purchase #2 $68.34   7.373%   $73.3787   $73.38   $73.40   $73.40  
  Purchase #3 $144.28   4.442%   $150.6889   $150.69   $150.70   $150.70  
  Purchase #4 $243.39   5.449%   $256.6523   $256.65   $256.65   $256.70  
  Purchase #5 $61.79   11.148%   $68.6783   $68.68   $68.70   $68.70  
  Purchase #6 $106.26   11.663%   $118.6531   $118.65   $118.65   $118.70  
  Purchase #7 $22.66   9.814%   $24.8839   $24.88   $24.90   $24.90  
  7 purchase totals = $801.69       $859.5063   $859.50   $859.55   $859.70