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 $46.36   8.223%   $50.1722   $50.17   $50.15   $50.20  
  Purchase #2 $198.39   7.201%   $212.6761   $212.68   $212.70   $212.70  
  Purchase #3 $174.62   13.331%   $197.8986   $197.90   $197.90   $197.90  
  Purchase #4 $149.95   7.130%   $160.6414   $160.64   $160.65   $160.60  
  Purchase #5 $165.56   11.313%   $184.2898   $184.29   $184.30   $184.30  
  Purchase #6 $65.85   6.318%   $70.0104   $70.01   $70.00   $70.00  
  Purchase #7 $25.74   10.676%   $28.488   $28.49   $28.50   $28.50  
  7 purchase totals = $826.47       $904.1765   $904.18   $904.20   $904.20