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 $83.75   8.200%   $90.6175   $90.62   $90.60   $90.60  
  Purchase #2 $236.55   11.653%   $264.1152   $264.12   $264.10   $264.10  
  Purchase #3 $93.43   3.165%   $96.3871   $96.39   $96.40   $96.40  
  Purchase #4 $241.91   10.489%   $267.2839   $267.28   $267.30   $267.30  
  Purchase #5 $182.27   10.303%   $201.0493   $201.05   $201.05   $201.00  
  Purchase #6 $90.41   6.146%   $95.9666   $95.97   $95.95   $96.00  
  Purchase #7 $38.75   13.258%   $43.8875   $43.89   $43.90   $43.90  
  7 purchase totals = $967.07       $1,059.3071   $1,059.32   $1,059.30   $1,059.30