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 $174.51   12.341%   $196.0463   $196.05   $196.05   $196.00  
  Purchase #2 $147.34   11.313%   $164.0086   $164.01   $164.00   $164.00  
  Purchase #3 $156.95   13.294%   $177.8149   $177.81   $177.80   $177.80  
  Purchase #4 $55.58   10.171%   $61.233   $61.23   $61.25   $61.20  
  Purchase #5 $63.32   8.474%   $68.6857   $68.69   $68.70   $68.70  
  Purchase #6 $113.29   10.198%   $124.8433   $124.84   $124.85   $124.80  
  Purchase #7 $217.78   13.421%   $247.0083   $247.01   $247.00   $247.00  
  7 purchase totals = $928.77       $1,039.6401   $1,039.64   $1,039.65   $1,039.50