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 $186.56   13.680%   $212.0814   $212.08   $212.10   $212.10  
  Purchase #2 $37.70   4.773%   $39.4994   $39.50   $39.50   $39.50  
  Purchase #3 $161.36   6.631%   $172.0598   $172.06   $172.05   $172.10  
  Purchase #4 $135.73   6.825%   $144.9936   $144.99   $145.00   $145.00  
  Purchase #5 $166.62   3.488%   $172.4317   $172.43   $172.45   $172.40  
  Purchase #6 $112.92   3.352%   $116.7051   $116.71   $116.70   $116.70  
  Purchase #7 $169.40   13.576%   $192.3977   $192.40   $192.40   $192.40  
  7 purchase totals = $970.29       $1,050.1687   $1,050.17   $1,050.20   $1,050.20