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 $59.68   12.197%   $66.9592   $66.96   $66.95   $67.00  
  Purchase #2 $89.87   6.732%   $95.92   $95.92   $95.90   $95.90  
  Purchase #3 $106.45   13.307%   $120.6153   $120.62   $120.60   $120.60  
  Purchase #4 $167.82   11.692%   $187.4415   $187.44   $187.45   $187.40  
  Purchase #5 $240.93   11.470%   $268.5647   $268.56   $268.55   $268.60  
  Purchase #6 $156.34   13.244%   $177.0457   $177.05   $177.05   $177.00  
  Purchase #7 $83.66   8.742%   $90.9736   $90.97   $90.95   $91.00  
  7 purchase totals = $904.75       $1,007.5200   $1,007.52   $1,007.45   $1,007.50