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 $91.64   3.295%   $94.6595   $94.66   $94.65   $94.70  
  Purchase #2 $67.69   11.317%   $75.3505   $75.35   $75.35   $75.40  
  Purchase #3 $203.90   8.333%   $220.891   $220.89   $220.90   $220.90  
  Purchase #4 $167.42   9.311%   $183.0085   $183.01   $183.00   $183.00  
  Purchase #5 $213.62   12.481%   $240.2819   $240.28   $240.30   $240.30  
  Purchase #6 $96.64   9.384%   $105.7087   $105.71   $105.70   $105.70  
  Purchase #7 $17.34   9.744%   $19.0296   $19.03   $19.05   $19.00  
  7 purchase totals = $858.25       $938.9297   $938.93   $938.95   $939.00