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 $61.92   6.608%   $66.0117   $66.01   $66.00   $66.00  
  Purchase #2 $160.35   12.339%   $180.1356   $180.14   $180.15   $180.10  
  Purchase #3 $58.89   6.418%   $62.6696   $62.67   $62.65   $62.70  
  Purchase #4 $192.28   10.126%   $211.7503   $211.75   $211.75   $211.80  
  Purchase #5 $145.58   13.473%   $165.194   $165.19   $165.20   $165.20  
  Purchase #6 $21.54   11.690%   $24.058   $24.06   $24.05   $24.10  
  Purchase #7 $160.89   4.151%   $167.5685   $167.57   $167.55   $167.60  
  7 purchase totals = $801.45       $877.3877   $877.39   $877.35   $877.50