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 $244.92   12.702%   $276.0297   $276.03   $276.05   $276.00  
  Purchase #2 $106.55   11.544%   $118.8501   $118.85   $118.85   $118.90  
  Purchase #3 $108.53   7.377%   $116.5363   $116.54   $116.55   $116.50  
  Purchase #4 $21.52   7.671%   $23.1708   $23.17   $23.15   $23.20  
  Purchase #5 $238.80   5.628%   $252.2397   $252.24   $252.25   $252.20  
  Purchase #6 $119.55   5.697%   $126.3608   $126.36   $126.35   $126.40  
  Purchase #7 $33.70   11.179%   $37.4673   $37.47   $37.45   $37.50  
  7 purchase totals = $873.57       $950.6547   $950.66   $950.65   $950.70