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 $193.75   13.708%   $220.3093   $220.31   $220.30   $220.30  
  Purchase #2 $18.63   5.702%   $19.6923   $19.69   $19.70   $19.70  
  Purchase #3 $198.65   11.135%   $220.7697   $220.77   $220.75   $220.80  
  Purchase #4 $32.58   7.322%   $34.9655   $34.97   $34.95   $35.00  
  Purchase #5 $165.84   7.845%   $178.8501   $178.85   $178.85   $178.90  
  Purchase #6 $214.76   7.354%   $230.5535   $230.55   $230.55   $230.60  
  Purchase #7 $143.84   8.815%   $156.5195   $156.52   $156.50   $156.50  
  7 purchase totals = $968.05       $1,061.6599   $1,061.66   $1,061.60   $1,061.80