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 $96.79   8.193%   $104.72   $104.72   $104.70   $104.70  
  Purchase #2 $52.99   3.676%   $54.9379   $54.94   $54.95   $54.90  
  Purchase #3 $53.36   7.257%   $57.2323   $57.23   $57.25   $57.20  
  Purchase #4 $118.29   7.129%   $126.7229   $126.72   $126.70   $126.70  
  Purchase #5 $218.29   11.508%   $243.4108   $243.41   $243.40   $243.40  
  Purchase #6 $73.76   13.156%   $83.4639   $83.46   $83.45   $83.50  
  Purchase #7 $206.96   8.768%   $225.1063   $225.11   $225.10   $225.10  
  7 purchase totals = $820.44       $895.5941   $895.59   $895.55   $895.50