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 $47.52   11.208%   $52.846   $52.85   $52.85   $52.80  
  Purchase #2 $65.50   12.198%   $73.4897   $73.49   $73.50   $73.50  
  Purchase #3 $21.44   7.679%   $23.0864   $23.09   $23.10   $23.10  
  Purchase #4 $163.54   5.835%   $173.0826   $173.08   $173.10   $173.10  
  Purchase #5 $165.35   8.583%   $179.542   $179.54   $179.55   $179.50  
  Purchase #6 $223.87   9.707%   $245.6011   $245.60   $245.60   $245.60  
  Purchase #7 $43.78   11.470%   $48.8016   $48.80   $48.80   $48.80  
  7 purchase totals = $731.00       $796.4494   $796.45   $796.50   $796.40