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 $106.28   3.490%   $109.9892   $109.99   $110.00   $110.00  
  Purchase #2 $77.93   4.385%   $81.3472   $81.35   $81.35   $81.30  
  Purchase #3 $25.99   10.801%   $28.7972   $28.80   $28.80   $28.80  
  Purchase #4 $149.60   7.604%   $160.9756   $160.98   $161.00   $161.00  
  Purchase #5 $52.40   7.523%   $56.3421   $56.34   $56.35   $56.30  
  Purchase #6 $56.26   13.142%   $63.6537   $63.65   $63.65   $63.70  
  Purchase #7 $48.53   11.605%   $54.1619   $54.16   $54.15   $54.20  
  7 purchase totals = $516.99       $555.2669   $555.27   $555.30   $555.30