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 $152.69   8.222%   $165.2442   $165.24   $165.25   $165.20  
  Purchase #2 $226.54   10.363%   $250.0163   $250.02   $250.00   $250.00  
  Purchase #3 $236.62   4.201%   $246.5604   $246.56   $246.55   $246.60  
  Purchase #4 $176.32   4.772%   $184.734   $184.73   $184.75   $184.70  
  Purchase #5 $201.56   4.402%   $210.4327   $210.43   $210.45   $210.40  
  Purchase #6 $122.29   6.673%   $130.4504   $130.45   $130.45   $130.50  
  Purchase #7 $136.73   9.624%   $149.8889   $149.89   $149.90   $149.90  
  7 purchase totals = $1,252.75       $1,337.3269   $1,337.32   $1,337.35   $1,337.30