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 $241.48   5.217%   $254.078   $254.08   $254.10   $254.10  
  Purchase #2 $161.32   8.322%   $174.7451   $174.75   $174.75   $174.70  
  Purchase #3 $56.30   4.103%   $58.61   $58.61   $58.60   $58.60  
  Purchase #4 $49.96   5.657%   $52.7862   $52.79   $52.80   $52.80  
  Purchase #5 $49.88   7.227%   $53.4848   $53.48   $53.50   $53.50  
  Purchase #6 $86.32   7.809%   $93.0607   $93.06   $93.05   $93.10  
  Purchase #7 $214.81   9.478%   $235.1697   $235.17   $235.15   $235.20  
  7 purchase totals = $860.07       $921.9345   $921.94   $921.95   $922.00