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 $166.65   8.585%   $180.9569   $180.96   $180.95   $181.00  
  Purchase #2 $175.86   8.617%   $191.0139   $191.01   $191.00   $191.00  
  Purchase #3 $90.76   7.410%   $97.4853   $97.49   $97.50   $97.50  
  Purchase #4 $206.86   11.688%   $231.0378   $231.04   $231.05   $231.00  
  Purchase #5 $235.50   13.268%   $266.7461   $266.75   $266.75   $266.70  
  Purchase #6 $90.75   5.566%   $95.8011   $95.80   $95.80   $95.80  
  Purchase #7 $64.46   11.640%   $71.9631   $71.96   $71.95   $72.00  
  7 purchase totals = $1,030.84       $1,135.0042   $1,135.01   $1,135.00   $1,135.00