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 $124.94   7.245%   $133.9919   $133.99   $134.00   $134.00  
  Purchase #2 $192.87   5.407%   $203.2985   $203.30   $203.30   $203.30  
  Purchase #3 $59.45   10.260%   $65.5496   $65.55   $65.55   $65.50  
  Purchase #4 $33.37   6.638%   $35.5851   $35.59   $35.60   $35.60  
  Purchase #5 $235.29   12.568%   $264.8612   $264.86   $264.85   $264.90  
  Purchase #6 $201.52   10.530%   $222.7401   $222.74   $222.75   $222.70  
  Purchase #7 $38.83   8.498%   $42.1298   $42.13   $42.15   $42.10  
  7 purchase totals = $886.27       $968.1562   $968.16   $968.20   $968.10