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 $87.62   10.201%   $96.5581   $96.56   $96.55   $96.60  
  Purchase #2 $80.68   13.139%   $91.2805   $91.28   $91.30   $91.30  
  Purchase #3 $10.72   12.825%   $12.0948   $12.09   $12.10   $12.10  
  Purchase #4 $203.86   12.221%   $228.7737   $228.77   $228.75   $228.80  
  Purchase #5 $250.36   11.306%   $278.6657   $278.67   $278.65   $278.70  
  Purchase #6 $176.29   11.242%   $196.1085   $196.11   $196.10   $196.10  
  Purchase #7 $24.66   3.748%   $25.5843   $25.58   $25.60   $25.60  
  7 purchase totals = $834.19       $929.0656   $929.06   $929.05   $929.20