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 $38.36   13.579%   $43.5689   $43.57   $43.55   $43.60  
  Purchase #2 $242.97   13.178%   $274.9886   $274.99   $275.00   $275.00  
  Purchase #3 $179.61   12.205%   $201.5314   $201.53   $201.55   $201.50  
  Purchase #4 $25.59   11.268%   $28.4735   $28.47   $28.45   $28.50  
  Purchase #5 $17.42   8.246%   $18.8565   $18.86   $18.85   $18.90  
  Purchase #6 $229.77   7.357%   $246.6742   $246.67   $246.65   $246.70  
  Purchase #7 $220.36   10.371%   $243.2135   $243.21   $243.20   $243.20  
  7 purchase totals = $954.08       $1,057.3066   $1,057.30   $1,057.25   $1,057.40