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 $25.34   12.582%   $28.5283   $28.53   $28.55   $28.50  
  Purchase #2 $45.77   5.462%   $48.27   $48.27   $48.25   $48.30  
  Purchase #3 $241.38   11.493%   $269.1218   $269.12   $269.10   $269.10  
  Purchase #4 $183.52   9.593%   $201.1251   $201.13   $201.15   $201.10  
  Purchase #5 $186.36   9.104%   $203.3262   $203.33   $203.35   $203.30  
  Purchase #6 $179.25   12.612%   $201.857   $201.86   $201.85   $201.90  
  Purchase #7 $201.99   7.298%   $216.7312   $216.73   $216.75   $216.70  
  7 purchase totals = $1,063.61       $1,168.9596   $1,168.97   $1,169.00   $1,168.90