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 $67.83   3.479%   $70.1898   $70.19   $70.20   $70.20  
  Purchase #2 $98.47   10.355%   $108.6666   $108.67   $108.65   $108.70  
  Purchase #3 $152.74   4.729%   $159.9631   $159.96   $159.95   $160.00  
  Purchase #4 $166.28   4.339%   $173.4949   $173.49   $173.50   $173.50  
  Purchase #5 $110.52   13.527%   $125.47   $125.47   $125.45   $125.50  
  Purchase #6 $235.97   5.714%   $249.4533   $249.45   $249.45   $249.50  
  Purchase #7 $193.94   8.824%   $211.0533   $211.05   $211.05   $211.10  
  7 purchase totals = $1,025.75       $1,098.2910   $1,098.28   $1,098.25   $1,098.50