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 $47.54   6.685%   $50.718   $50.72   $50.70   $50.70  
  Purchase #2 $155.99   12.681%   $175.7711   $175.77   $175.75   $175.80  
  Purchase #3 $61.71   12.131%   $69.196   $69.20   $69.20   $69.20  
  Purchase #4 $194.54   5.144%   $204.5471   $204.55   $204.55   $204.50  
  Purchase #5 $229.71   5.173%   $241.5929   $241.59   $241.60   $241.60  
  Purchase #6 $229.47   9.508%   $251.288   $251.29   $251.30   $251.30  
  Purchase #7 $52.41   11.782%   $58.5849   $58.58   $58.60   $58.60  
  7 purchase totals = $971.37       $1,051.6980   $1,051.70   $1,051.70   $1,051.70