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 $143.71   4.446%   $150.0993   $150.10   $150.10   $150.10  
  Purchase #2 $26.80   6.284%   $28.4841   $28.48   $28.50   $28.50  
  Purchase #3 $11.30   6.658%   $12.0524   $12.05   $12.05   $12.10  
  Purchase #4 $129.55   13.567%   $147.126   $147.13   $147.15   $147.10  
  Purchase #5 $205.32   11.829%   $229.6073   $229.61   $229.60   $229.60  
  Purchase #6 $101.44   8.457%   $110.0188   $110.02   $110.00   $110.00  
  Purchase #7 $90.70   13.221%   $102.6914   $102.69   $102.70   $102.70  
  7 purchase totals = $708.82       $780.0793   $780.08   $780.10   $780.10