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 $162.47   8.327%   $175.9989   $176.00   $176.00   $176.00  
  Purchase #2 $6.92   13.429%   $7.8493   $7.85   $7.85   $7.80  
  Purchase #3 $79.45   10.263%   $87.604   $87.60   $87.60   $87.60  
  Purchase #4 $29.84   5.793%   $31.5686   $31.57   $31.55   $31.60  
  Purchase #5 $239.53   11.225%   $266.4172   $266.42   $266.40   $266.40  
  Purchase #6 $192.29   6.177%   $204.1678   $204.17   $204.15   $204.20  
  Purchase #7 $200.76   9.731%   $220.296   $220.30   $220.30   $220.30  
  7 purchase totals = $911.26       $993.9018   $993.91   $993.85   $993.90