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 $168.71   4.642%   $176.5415   $176.54   $176.55   $176.50  
  Purchase #2 $150.99   13.493%   $171.3631   $171.36   $171.35   $171.40  
  Purchase #3 $73.90   13.657%   $83.9925   $83.99   $84.00   $84.00  
  Purchase #4 $168.90   4.868%   $177.1221   $177.12   $177.10   $177.10  
  Purchase #5 $99.40   11.192%   $110.5248   $110.52   $110.50   $110.50  
  Purchase #6 $174.67   9.199%   $190.7379   $190.74   $190.75   $190.70  
  Purchase #7 $220.33   13.791%   $250.7157   $250.72   $250.70   $250.70  
  7 purchase totals = $1,056.90       $1,160.9976   $1,160.99   $1,160.95   $1,160.90