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 $14.72   13.155%   $16.6564   $16.66   $16.65   $16.70  
  Purchase #2 $221.41   10.241%   $244.0846   $244.08   $244.10   $244.10  
  Purchase #3 $158.39   10.457%   $174.9528   $174.95   $174.95   $175.00  
  Purchase #4 $69.85   7.203%   $74.8813   $74.88   $74.90   $74.90  
  Purchase #5 $120.98   5.297%   $127.3883   $127.39   $127.40   $127.40  
  Purchase #6 $193.87   8.212%   $209.7906   $209.79   $209.80   $209.80  
  Purchase #7 $196.58   13.495%   $223.1085   $223.11   $223.10   $223.10  
  7 purchase totals = $975.80       $1,070.8625   $1,070.86   $1,070.90   $1,071.00