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 $103.53   13.288%   $117.2871   $117.29   $117.30   $117.30  
  Purchase #2 $241.43   4.246%   $251.6811   $251.68   $251.70   $251.70  
  Purchase #3 $232.79   4.225%   $242.6254   $242.63   $242.65   $242.60  
  Purchase #4 $150.55   10.803%   $166.8139   $166.81   $166.80   $166.80  
  Purchase #5 $53.86   4.628%   $56.3526   $56.35   $56.35   $56.40  
  Purchase #6 $38.28   5.642%   $40.4398   $40.44   $40.45   $40.40  
  Purchase #7 $45.46   5.102%   $47.7794   $47.78   $47.80   $47.80  
  7 purchase totals = $865.90       $922.9793   $922.98   $923.05   $923.00