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 $49.77   9.850%   $54.6723   $54.67   $54.65   $54.70  
  Purchase #2 $144.84   4.579%   $151.4722   $151.47   $151.45   $151.50  
  Purchase #3 $95.93   3.381%   $99.1734   $99.17   $99.15   $99.20  
  Purchase #4 $75.70   11.492%   $84.3994   $84.40   $84.40   $84.40  
  Purchase #5 $50.35   10.727%   $55.751   $55.75   $55.75   $55.80  
  Purchase #6 $212.89   6.226%   $226.1445   $226.14   $226.15   $226.10  
  Purchase #7 $235.57   12.195%   $264.2978   $264.30   $264.30   $264.30  
  7 purchase totals = $865.05       $935.9106   $935.90   $935.85   $936.00