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 $163.28   11.215%   $181.5919   $181.59   $181.60   $181.60  
  Purchase #2 $242.75   9.249%   $265.2019   $265.20   $265.20   $265.20  
  Purchase #3 $211.42   11.286%   $235.2809   $235.28   $235.30   $235.30  
  Purchase #4 $13.99   3.865%   $14.5307   $14.53   $14.55   $14.50  
  Purchase #5 $134.91   5.816%   $142.7564   $142.76   $142.75   $142.80  
  Purchase #6 $59.57   8.762%   $64.7895   $64.79   $64.80   $64.80  
  Purchase #7 $28.38   10.550%   $31.3741   $31.37   $31.35   $31.40  
  7 purchase totals = $854.30       $935.5254   $935.52   $935.55   $935.60