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 $75.59   12.470%   $85.0161   $85.02   $85.00   $85.00  
  Purchase #2 $135.92   6.440%   $144.6732   $144.67   $144.65   $144.70  
  Purchase #3 $90.84   5.763%   $96.0751   $96.08   $96.10   $96.10  
  Purchase #4 $111.99   6.682%   $119.4732   $119.47   $119.45   $119.50  
  Purchase #5 $26.70   10.566%   $29.5211   $29.52   $29.50   $29.50  
  Purchase #6 $64.65   13.768%   $73.551   $73.55   $73.55   $73.60  
  Purchase #7 $186.35   9.786%   $204.5862   $204.59   $204.60   $204.60  
  7 purchase totals = $692.04       $752.8959   $752.90   $752.85   $753.00