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 $130.73   13.255%   $148.0583   $148.06   $148.05   $148.10  
  Purchase #2 $169.36   4.828%   $177.5367   $177.54   $177.55   $177.50  
  Purchase #3 $214.38   13.387%   $243.0791   $243.08   $243.10   $243.10  
  Purchase #4 $34.72   13.717%   $39.4825   $39.48   $39.50   $39.50  
  Purchase #5 $98.45   11.397%   $109.6703   $109.67   $109.65   $109.70  
  Purchase #6 $61.93   6.236%   $65.792   $65.79   $65.80   $65.80  
  Purchase #7 $10.36   10.823%   $11.4813   $11.48   $11.50   $11.50  
  7 purchase totals = $719.93       $795.1002   $795.10   $795.15   $795.20