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 $239.96   11.463%   $267.4666   $267.47   $267.45   $267.50  
  Purchase #2 $93.81   11.606%   $104.6976   $104.70   $104.70   $104.70  
  Purchase #3 $147.95   8.247%   $160.1514   $160.15   $160.15   $160.20  
  Purchase #4 $142.42   3.148%   $146.9034   $146.90   $146.90   $146.90  
  Purchase #5 $14.84   3.245%   $15.3216   $15.32   $15.30   $15.30  
  Purchase #6 $27.44   4.313%   $28.6235   $28.62   $28.60   $28.60  
  Purchase #7 $129.77   6.353%   $138.0143   $138.01   $138.00   $138.00  
  7 purchase totals = $796.19       $861.1784   $861.17   $861.10   $861.20