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 $137.95   10.388%   $152.2802   $152.28   $152.30   $152.30  
  Purchase #2 $156.90   4.169%   $163.4412   $163.44   $163.45   $163.40  
  Purchase #3 $57.36   10.753%   $63.5279   $63.53   $63.55   $63.50  
  Purchase #4 $247.28   8.487%   $268.2667   $268.27   $268.25   $268.30  
  Purchase #5 $61.91   11.308%   $68.9108   $68.91   $68.90   $68.90  
  Purchase #6 $92.80   3.267%   $95.8318   $95.83   $95.85   $95.80  
  Purchase #7 $192.83   4.125%   $200.7842   $200.78   $200.80   $200.80  
  7 purchase totals = $947.03       $1,013.0428   $1,013.04   $1,013.10   $1,013.00