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 $198.87   10.608%   $219.9661   $219.97   $219.95   $220.00  
  Purchase #2 $226.44   11.273%   $251.9666   $251.97   $251.95   $252.00  
  Purchase #3 $24.48   13.824%   $27.8641   $27.86   $27.85   $27.90  
  Purchase #4 $60.80   12.727%   $68.538   $68.54   $68.55   $68.50  
  Purchase #5 $242.51   11.463%   $270.3089   $270.31   $270.30   $270.30  
  Purchase #6 $82.60   7.179%   $88.5299   $88.53   $88.55   $88.50  
  Purchase #7 $59.35   9.106%   $64.7544   $64.75   $64.75   $64.80  
  7 purchase totals = $895.05       $991.9280   $991.93   $991.90   $992.00