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 $38.83   10.526%   $42.9172   $42.92   $42.90   $42.90  
  Purchase #2 $169.40   6.448%   $180.3229   $180.32   $180.30   $180.30  
  Purchase #3 $203.59   5.124%   $214.022   $214.02   $214.00   $214.00  
  Purchase #4 $143.75   11.857%   $160.7944   $160.79   $160.80   $160.80  
  Purchase #5 $43.88   4.406%   $45.8134   $45.81   $45.80   $45.80  
  Purchase #6 $241.52   3.595%   $250.2026   $250.20   $250.20   $250.20  
  Purchase #7 $158.98   9.787%   $174.5394   $174.54   $174.55   $174.50  
  7 purchase totals = $999.95       $1,068.6119   $1,068.60   $1,068.55   $1,068.50