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 $235.84   12.863%   $266.1761   $266.18   $266.20   $266.20  
  Purchase #2 $138.48   4.415%   $144.5939   $144.59   $144.60   $144.60  
  Purchase #3 $43.58   3.689%   $45.1877   $45.19   $45.20   $45.20  
  Purchase #4 $15.31   7.156%   $16.4056   $16.41   $16.40   $16.40  
  Purchase #5 $50.85   11.613%   $56.7552   $56.76   $56.75   $56.80  
  Purchase #6 $130.35   10.696%   $144.2922   $144.29   $144.30   $144.30  
  Purchase #7 $160.77   12.560%   $180.9627   $180.96   $180.95   $181.00  
  7 purchase totals = $775.18       $854.3734   $854.38   $854.40   $854.50