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 $45.65   8.540%   $49.5485   $49.55   $49.55   $49.50  
  Purchase #2 $87.68   5.772%   $92.7409   $92.74   $92.75   $92.70  
  Purchase #3 $95.32   8.398%   $103.325   $103.33   $103.35   $103.30  
  Purchase #4 $207.91   7.553%   $223.6134   $223.61   $223.60   $223.60  
  Purchase #5 $192.98   5.665%   $203.9123   $203.91   $203.90   $203.90  
  Purchase #6 $250.91   6.153%   $266.3485   $266.35   $266.35   $266.30  
  Purchase #7 $82.65   5.811%   $87.4528   $87.45   $87.45   $87.50  
  7 purchase totals = $963.10       $1,026.9414   $1,026.94   $1,026.95   $1,026.80