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 $149.98   10.211%   $165.2945   $165.29   $165.30   $165.30  
  Purchase #2 $77.32   13.268%   $87.5788   $87.58   $87.60   $87.60  
  Purchase #3 $48.93   5.565%   $51.653   $51.65   $51.65   $51.70  
  Purchase #4 $171.58   11.625%   $191.5262   $191.53   $191.55   $191.50  
  Purchase #5 $204.82   10.484%   $226.2933   $226.29   $226.30   $226.30  
  Purchase #6 $57.90   6.283%   $61.5379   $61.54   $61.55   $61.50  
  Purchase #7 $235.84   9.406%   $258.0231   $258.02   $258.00   $258.00  
  7 purchase totals = $946.37       $1,041.9068   $1,041.90   $1,041.95   $1,041.90