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 $126.92   5.672%   $134.1189   $134.12   $134.10   $134.10  
  Purchase #2 $58.87   9.142%   $64.2519   $64.25   $64.25   $64.30  
  Purchase #3 $44.80   8.755%   $48.7222   $48.72   $48.70   $48.70  
  Purchase #4 $222.49   12.647%   $250.6283   $250.63   $250.65   $250.60  
  Purchase #5 $201.75   6.334%   $214.5288   $214.53   $214.55   $214.50  
  Purchase #6 $101.27   11.104%   $112.515   $112.52   $112.50   $112.50  
  Purchase #7 $220.60   9.186%   $240.8643   $240.86   $240.85   $240.90  
  7 purchase totals = $976.70       $1,065.6294   $1,065.63   $1,065.60   $1,065.60