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 $48.90   5.454%   $51.567   $51.57   $51.55   $51.60  
  Purchase #2 $249.48   8.168%   $269.8575   $269.86   $269.85   $269.90  
  Purchase #3 $145.27   3.413%   $150.2281   $150.23   $150.25   $150.20  
  Purchase #4 $208.53   11.502%   $232.5151   $232.52   $232.50   $232.50  
  Purchase #5 $185.43   13.254%   $210.0069   $210.01   $210.00   $210.00  
  Purchase #6 $179.42   4.364%   $187.2499   $187.25   $187.25   $187.20  
  Purchase #7 $243.41   7.740%   $262.2499   $262.25   $262.25   $262.20  
  7 purchase totals = $1,260.44       $1,363.6744   $1,363.69   $1,363.65   $1,363.60