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 $49.98   8.463%   $54.2098   $54.21   $54.20   $54.20  
  Purchase #2 $33.72   11.753%   $37.6831   $37.68   $37.70   $37.70  
  Purchase #3 $22.55   7.330%   $24.2029   $24.20   $24.20   $24.20  
  Purchase #4 $132.73   9.511%   $145.354   $145.35   $145.35   $145.40  
  Purchase #5 $245.77   8.723%   $267.2085   $267.21   $267.20   $267.20  
  Purchase #6 $222.85   11.764%   $249.0661   $249.07   $249.05   $249.10  
  Purchase #7 $16.52   4.599%   $17.2798   $17.28   $17.30   $17.30  
  7 purchase totals = $724.12       $795.0042   $795.00   $795.00   $795.10