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 $187.27   12.768%   $211.1806   $211.18   $211.20   $211.20  
  Purchase #2 $24.64   8.396%   $26.7088   $26.71   $26.70   $26.70  
  Purchase #3 $45.42   4.239%   $47.3454   $47.35   $47.35   $47.30  
  Purchase #4 $160.49   9.645%   $175.9693   $175.97   $175.95   $176.00  
  Purchase #5 $246.52   9.331%   $269.5228   $269.52   $269.50   $269.50  
  Purchase #6 $160.36   3.688%   $166.2741   $166.27   $166.25   $166.30  
  Purchase #7 $248.72   7.648%   $267.7421   $267.74   $267.75   $267.70  
  7 purchase totals = $1,073.42       $1,164.7431   $1,164.74   $1,164.70   $1,164.70