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 $186.84   3.576%   $193.5214   $193.52   $193.50   $193.50  
  Purchase #2 $33.44   3.751%   $34.6943   $34.69   $34.70   $34.70  
  Purchase #3 $226.35   9.621%   $248.1271   $248.13   $248.15   $248.10  
  Purchase #4 $239.84   6.579%   $255.6191   $255.62   $255.60   $255.60  
  Purchase #5 $158.71   9.130%   $173.2002   $173.20   $173.20   $173.20  
  Purchase #6 $126.80   11.518%   $141.4048   $141.40   $141.40   $141.40  
  Purchase #7 $145.83   10.174%   $160.6667   $160.67   $160.65   $160.70  
  7 purchase totals = $1,117.81       $1,207.2336   $1,207.23   $1,207.20   $1,207.20