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 $194.79   13.387%   $220.8665   $220.87   $220.85   $220.90  
  Purchase #2 $140.54   11.540%   $156.7583   $156.76   $156.75   $156.80  
  Purchase #3 $155.77   12.215%   $174.7973   $174.80   $174.80   $174.80  
  Purchase #4 $124.42   9.194%   $135.8592   $135.86   $135.85   $135.90  
  Purchase #5 $232.80   6.348%   $247.5781   $247.58   $247.60   $247.60  
  Purchase #6 $52.71   5.332%   $55.5205   $55.52   $55.50   $55.50  
  Purchase #7 $96.25   8.475%   $104.4072   $104.41   $104.40   $104.40  
  7 purchase totals = $997.28       $1,095.7871   $1,095.80   $1,095.75   $1,095.90