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 $227.52   8.270%   $246.3359   $246.34   $246.35   $246.30  
  Purchase #2 $185.91   4.425%   $194.1365   $194.14   $194.15   $194.10  
  Purchase #3 $196.44   10.411%   $216.8914   $216.89   $216.90   $216.90  
  Purchase #4 $77.62   3.782%   $80.5556   $80.56   $80.55   $80.60  
  Purchase #5 $236.82   3.462%   $245.0187   $245.02   $245.00   $245.00  
  Purchase #6 $160.49   3.319%   $165.8167   $165.82   $165.80   $165.80  
  Purchase #7 $109.64   6.391%   $116.6471   $116.65   $116.65   $116.60  
  7 purchase totals = $1,194.44       $1,265.4019   $1,265.42   $1,265.40   $1,265.30