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 $76.52   13.529%   $86.8724   $86.87   $86.85   $86.90  
  Purchase #2 $49.97   6.182%   $53.0591   $53.06   $53.05   $53.10  
  Purchase #3 $227.53   3.326%   $235.0976   $235.10   $235.10   $235.10  
  Purchase #4 $147.56   5.130%   $155.1298   $155.13   $155.15   $155.10  
  Purchase #5 $229.58   6.866%   $245.343   $245.34   $245.35   $245.30  
  Purchase #6 $227.28   8.706%   $247.067   $247.07   $247.05   $247.10  
  Purchase #7 $137.42   9.617%   $150.6357   $150.64   $150.65   $150.60  
  7 purchase totals = $1,095.86       $1,173.2046   $1,173.21   $1,173.20   $1,173.20