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 $87.88   5.588%   $92.7907   $92.79   $92.80   $92.80  
  Purchase #2 $56.65   7.640%   $60.9781   $60.98   $61.00   $61.00  
  Purchase #3 $78.45   9.578%   $85.9639   $85.96   $85.95   $86.00  
  Purchase #4 $227.75   9.278%   $248.8806   $248.88   $248.90   $248.90  
  Purchase #5 $58.30   13.546%   $66.1973   $66.20   $66.20   $66.20  
  Purchase #6 $54.59   10.435%   $60.2865   $60.29   $60.30   $60.30  
  Purchase #7 $168.90   6.629%   $180.0964   $180.10   $180.10   $180.10  
  7 purchase totals = $732.52       $795.1935   $795.20   $795.25   $795.30