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 $80.77   13.847%   $91.9542   $91.95   $91.95   $92.00  
  Purchase #2 $220.28   11.832%   $246.3435   $246.34   $246.35   $246.30  
  Purchase #3 $183.96   9.661%   $201.7324   $201.73   $201.75   $201.70  
  Purchase #4 $52.37   7.220%   $56.1511   $56.15   $56.15   $56.20  
  Purchase #5 $46.87   6.296%   $49.8209   $49.82   $49.80   $49.80  
  Purchase #6 $183.67   8.546%   $199.3664   $199.37   $199.35   $199.40  
  Purchase #7 $21.66   4.528%   $22.6408   $22.64   $22.65   $22.60  
  7 purchase totals = $789.58       $868.0093   $868.00   $868.00   $868.00