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 $38.58   12.688%   $43.475   $43.48   $43.50   $43.50  
  Purchase #2 $77.37   13.523%   $87.8327   $87.83   $87.85   $87.80  
  Purchase #3 $113.55   10.126%   $125.0481   $125.05   $125.05   $125.00  
  Purchase #4 $200.90   5.818%   $212.5884   $212.59   $212.60   $212.60  
  Purchase #5 $96.92   6.187%   $102.9164   $102.92   $102.90   $102.90  
  Purchase #6 $164.92   6.134%   $175.0362   $175.04   $175.05   $175.00  
  Purchase #7 $120.75   5.474%   $127.3599   $127.36   $127.35   $127.40  
  7 purchase totals = $812.99       $874.2567   $874.27   $874.30   $874.20