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 $55.38   12.562%   $62.3368   $62.34   $62.35   $62.30  
  Purchase #2 $93.56   9.104%   $102.0777   $102.08   $102.10   $102.10  
  Purchase #3 $110.65   12.850%   $124.8685   $124.87   $124.85   $124.90  
  Purchase #4 $55.64   10.682%   $61.5835   $61.58   $61.60   $61.60  
  Purchase #5 $81.34   5.489%   $85.8048   $85.80   $85.80   $85.80  
  Purchase #6 $205.59   9.769%   $225.6741   $225.67   $225.65   $225.70  
  Purchase #7 $31.43   7.178%   $33.686   $33.69   $33.70   $33.70  
  7 purchase totals = $633.59       $696.0314   $696.03   $696.05   $696.10