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 $205.48   13.604%   $233.4335   $233.43   $233.45   $233.40  
  Purchase #2 $153.54   7.642%   $165.2735   $165.27   $165.25   $165.30  
  Purchase #3 $157.48   11.293%   $175.2642   $175.26   $175.25   $175.30  
  Purchase #4 $191.63   5.363%   $201.9071   $201.91   $201.90   $201.90  
  Purchase #5 $202.74   5.529%   $213.9495   $213.95   $213.95   $213.90  
  Purchase #6 $48.36   8.667%   $52.5514   $52.55   $52.55   $52.60  
  Purchase #7 $202.96   11.854%   $227.0189   $227.02   $227.00   $227.00  
  7 purchase totals = $1,162.19       $1,269.3981   $1,269.39   $1,269.35   $1,269.40