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 $170.91   5.157%   $179.7238   $179.72   $179.70   $179.70  
  Purchase #2 $17.31   11.788%   $19.3505   $19.35   $19.35   $19.40  
  Purchase #3 $68.72   6.568%   $73.2335   $73.23   $73.25   $73.20  
  Purchase #4 $58.67   10.487%   $64.8227   $64.82   $64.80   $64.80  
  Purchase #5 $245.72   3.731%   $254.8878   $254.89   $254.90   $254.90  
  Purchase #6 $192.33   3.158%   $198.4038   $198.40   $198.40   $198.40  
  Purchase #7 $61.40   3.584%   $63.6006   $63.60   $63.60   $63.60  
  7 purchase totals = $815.06       $854.0227   $854.01   $854.00   $854.00