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 $176.83   5.612%   $186.7537   $186.75   $186.75   $186.80  
  Purchase #2 $194.93   6.855%   $208.2925   $208.29   $208.30   $208.30  
  Purchase #3 $112.28   5.819%   $118.8136   $118.81   $118.80   $118.80  
  Purchase #4 $144.56   12.426%   $162.523   $162.52   $162.50   $162.50  
  Purchase #5 $88.33   5.767%   $93.424   $93.42   $93.40   $93.40  
  Purchase #6 $58.78   3.448%   $60.8067   $60.81   $60.80   $60.80  
  Purchase #7 $184.32   11.637%   $205.7693   $205.77   $205.75   $205.80  
  7 purchase totals = $960.03       $1,036.3828   $1,036.37   $1,036.30   $1,036.40