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 $146.25   10.211%   $161.1836   $161.18   $161.20   $161.20  
  Purchase #2 $16.26   8.150%   $17.5852   $17.59   $17.60   $17.60  
  Purchase #3 $188.50   8.561%   $204.6375   $204.64   $204.65   $204.60  
  Purchase #4 $73.50   7.310%   $78.8729   $78.87   $78.85   $78.90  
  Purchase #5 $150.97   9.474%   $165.2729   $165.27   $165.25   $165.30  
  Purchase #6 $208.90   9.268%   $228.2609   $228.26   $228.25   $228.30  
  Purchase #7 $56.93   3.218%   $58.762   $58.76   $58.75   $58.80  
  7 purchase totals = $841.31       $914.5750   $914.57   $914.55   $914.70