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 $34.77   6.350%   $36.9779   $36.98   $37.00   $37.00  
  Purchase #2 $90.69   9.388%   $99.204   $99.20   $99.20   $99.20  
  Purchase #3 $16.77   8.154%   $18.1374   $18.14   $18.15   $18.10  
  Purchase #4 $171.32   12.194%   $192.2108   $192.21   $192.20   $192.20  
  Purchase #5 $232.35   6.152%   $246.6442   $246.64   $246.65   $246.60  
  Purchase #6 $130.30   6.162%   $138.3291   $138.33   $138.35   $138.30  
  Purchase #7 $36.88   10.560%   $40.7745   $40.77   $40.75   $40.80  
  7 purchase totals = $713.08       $772.2779   $772.27   $772.30   $772.20