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 $193.39   6.142%   $205.268   $205.27   $205.25   $205.30  
  Purchase #2 $21.44   12.288%   $24.0745   $24.07   $24.05   $24.10  
  Purchase #3 $209.66   13.529%   $238.0249   $238.02   $238.00   $238.00  
  Purchase #4 $68.88   4.479%   $71.9651   $71.97   $71.95   $72.00  
  Purchase #5 $200.53   11.221%   $223.0315   $223.03   $223.05   $223.00  
  Purchase #6 $156.92   5.831%   $166.07   $166.07   $166.05   $166.10  
  Purchase #7 $241.66   3.644%   $250.4661   $250.47   $250.45   $250.50  
  7 purchase totals = $1,092.48       $1,178.9001   $1,178.90   $1,178.80   $1,179.00