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 $174.79   8.808%   $190.1855   $190.19   $190.20   $190.20  
  Purchase #2 $189.34   6.484%   $201.6168   $201.62   $201.60   $201.60  
  Purchase #3 $121.28   13.856%   $138.0846   $138.08   $138.10   $138.10  
  Purchase #4 $241.42   6.236%   $256.475   $256.48   $256.50   $256.50  
  Purchase #5 $232.44   4.793%   $243.5808   $243.58   $243.60   $243.60  
  Purchase #6 $182.26   3.255%   $188.1926   $188.19   $188.20   $188.20  
  Purchase #7 $50.76   13.502%   $57.6136   $57.61   $57.60   $57.60  
  7 purchase totals = $1,192.29       $1,275.7489   $1,275.75   $1,275.80   $1,275.80