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 $176.53   7.416%   $189.6215   $189.62   $189.60   $189.60  
  Purchase #2 $63.33   5.184%   $66.613   $66.61   $66.60   $66.60  
  Purchase #3 $25.45   7.355%   $27.3218   $27.32   $27.30   $27.30  
  Purchase #4 $211.97   3.542%   $219.478   $219.48   $219.50   $219.50  
  Purchase #5 $191.71   5.249%   $201.7729   $201.77   $201.75   $201.80  
  Purchase #6 $179.41   4.601%   $187.6647   $187.66   $187.65   $187.70  
  Purchase #7 $218.69   7.239%   $234.521   $234.52   $234.50   $234.50  
  7 purchase totals = $1,067.09       $1,126.9929   $1,126.98   $1,126.90   $1,127.00