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 $71.99   6.186%   $76.4433   $76.44   $76.45   $76.40  
  Purchase #2 $61.57   6.654%   $65.6669   $65.67   $65.65   $65.70  
  Purchase #3 $100.87   3.225%   $104.1231   $104.12   $104.10   $104.10  
  Purchase #4 $249.49   5.222%   $262.5184   $262.52   $262.50   $262.50  
  Purchase #5 $220.68   4.112%   $229.7544   $229.75   $229.75   $229.80  
  Purchase #6 $139.34   4.546%   $145.6744   $145.67   $145.65   $145.70  
  Purchase #7 $29.41   8.654%   $31.9551   $31.96   $31.95   $32.00  
  7 purchase totals = $873.35       $916.1356   $916.13   $916.05   $916.20