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 $54.37   5.369%   $57.2891   $57.29   $57.30   $57.30  
  Purchase #2 $229.33   10.564%   $253.5564   $253.56   $253.55   $253.60  
  Purchase #3 $150.51   12.419%   $169.2018   $169.20   $169.20   $169.20  
  Purchase #4 $50.27   5.544%   $53.057   $53.06   $53.05   $53.10  
  Purchase #5 $172.26   8.159%   $186.3147   $186.31   $186.30   $186.30  
  Purchase #6 $61.57   7.145%   $65.9692   $65.97   $65.95   $66.00  
  Purchase #7 $170.27   8.678%   $185.046   $185.05   $185.05   $185.00  
  7 purchase totals = $888.58       $970.4342   $970.44   $970.40   $970.50