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 $203.92   7.284%   $218.7735   $218.77   $218.75   $218.80  
  Purchase #2 $33.49   13.335%   $37.9559   $37.96   $37.95   $38.00  
  Purchase #3 $62.39   4.714%   $65.3311   $65.33   $65.35   $65.30  
  Purchase #4 $167.69   6.108%   $177.9325   $177.93   $177.95   $177.90  
  Purchase #5 $239.34   4.540%   $250.206   $250.21   $250.20   $250.20  
  Purchase #6 $166.87   12.696%   $188.0558   $188.06   $188.05   $188.10  
  Purchase #7 $114.84   4.266%   $119.7391   $119.74   $119.75   $119.70  
  7 purchase totals = $988.54       $1,057.9939   $1,058.00   $1,058.00   $1,058.00