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 $48.66   12.192%   $54.5926   $54.59   $54.60   $54.60  
  Purchase #2 $165.37   7.828%   $178.3152   $178.32   $178.30   $178.30  
  Purchase #3 $73.96   6.749%   $78.9516   $78.95   $78.95   $79.00  
  Purchase #4 $194.65   4.330%   $203.0783   $203.08   $203.10   $203.10  
  Purchase #5 $13.49   10.759%   $14.9414   $14.94   $14.95   $14.90  
  Purchase #6 $183.58   11.230%   $204.196   $204.20   $204.20   $204.20  
  Purchase #7 $95.87   6.186%   $101.8005   $101.80   $101.80   $101.80  
  7 purchase totals = $775.58       $835.8756   $835.88   $835.90   $835.90