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 $217.70   3.701%   $225.7571   $225.76   $225.75   $225.80  
  Purchase #2 $106.38   5.267%   $111.983   $111.98   $112.00   $112.00  
  Purchase #3 $165.34   4.280%   $172.4166   $172.42   $172.40   $172.40  
  Purchase #4 $24.85   11.174%   $27.6267   $27.63   $27.65   $27.60  
  Purchase #5 $222.50   10.588%   $246.0583   $246.06   $246.05   $246.10  
  Purchase #6 $16.74   5.538%   $17.6671   $17.67   $17.65   $17.70  
  Purchase #7 $220.76   7.236%   $236.7342   $236.73   $236.75   $236.70  
  7 purchase totals = $974.27       $1,038.2430   $1,038.25   $1,038.25   $1,038.30