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 $196.77   11.295%   $218.9952   $219.00   $219.00   $219.00  
  Purchase #2 $158.45   5.350%   $166.9271   $166.93   $166.95   $166.90  
  Purchase #3 $154.97   11.860%   $173.3494   $173.35   $173.35   $173.30  
  Purchase #4 $163.52   12.541%   $184.027   $184.03   $184.05   $184.00  
  Purchase #5 $58.86   11.262%   $65.4888   $65.49   $65.50   $65.50  
  Purchase #6 $128.56   6.860%   $137.3792   $137.38   $137.40   $137.40  
  Purchase #7 $209.85   10.274%   $231.41   $231.41   $231.40   $231.40  
  7 purchase totals = $1,070.98       $1,177.5767   $1,177.59   $1,177.65   $1,177.50