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 $43.82   10.168%   $48.2756   $48.28   $48.30   $48.30  
  Purchase #2 $228.65   9.349%   $250.0265   $250.03   $250.05   $250.00  
  Purchase #3 $5.53   4.413%   $5.774   $5.77   $5.75   $5.80  
  Purchase #4 $204.58   3.387%   $211.5091   $211.51   $211.50   $211.50  
  Purchase #5 $169.84   11.852%   $189.9694   $189.97   $189.95   $190.00  
  Purchase #6 $56.58   7.258%   $60.6866   $60.69   $60.70   $60.70  
  Purchase #7 $154.79   5.304%   $163.0001   $163.00   $163.00   $163.00  
  7 purchase totals = $863.79       $929.2413   $929.25   $929.25   $929.30