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 $183.97   5.865%   $194.7598   $194.76   $194.75   $194.80  
  Purchase #2 $219.32   11.172%   $243.8224   $243.82   $243.80   $243.80  
  Purchase #3 $203.36   11.180%   $226.0956   $226.10   $226.10   $226.10  
  Purchase #4 $243.96   12.419%   $274.2574   $274.26   $274.25   $274.30  
  Purchase #5 $214.56   6.827%   $229.208   $229.21   $229.20   $229.20  
  Purchase #6 $50.28   8.726%   $54.6674   $54.67   $54.65   $54.70  
  Purchase #7 $106.96   13.133%   $121.0071   $121.01   $121.00   $121.00  
  7 purchase totals = $1,222.41       $1,343.8177   $1,343.83   $1,343.75   $1,343.90