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 $83.42   6.265%   $88.6463   $88.65   $88.65   $88.60  
  Purchase #2 $246.98   9.352%   $270.0776   $270.08   $270.10   $270.10  
  Purchase #3 $144.82   13.857%   $164.8877   $164.89   $164.90   $164.90  
  Purchase #4 $152.69   11.209%   $169.805   $169.81   $169.80   $169.80  
  Purchase #5 $242.57   12.541%   $272.9907   $272.99   $273.00   $273.00  
  Purchase #6 $188.81   7.833%   $203.5995   $203.60   $203.60   $203.60  
  Purchase #7 $136.30   12.680%   $153.5828   $153.58   $153.60   $153.60  
  7 purchase totals = $1,195.59       $1,323.5896   $1,323.60   $1,323.65   $1,323.60