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 $209.48   8.260%   $226.783   $226.78   $226.80   $226.80  
  Purchase #2 $212.55   11.640%   $237.2908   $237.29   $237.30   $237.30  
  Purchase #3 $111.58   8.416%   $120.9706   $120.97   $120.95   $121.00  
  Purchase #4 $120.52   4.759%   $126.2555   $126.26   $126.25   $126.30  
  Purchase #5 $211.30   13.363%   $239.536   $239.54   $239.55   $239.50  
  Purchase #6 $240.86   10.390%   $265.8854   $265.89   $265.90   $265.90  
  Purchase #7 $5.99   13.343%   $6.7892   $6.79   $6.80   $6.80  
  7 purchase totals = $1,112.28       $1,223.5105   $1,223.52   $1,223.55   $1,223.60