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 $53.57   11.286%   $59.6159   $59.62   $59.60   $59.60  
  Purchase #2 $24.50   13.812%   $27.8839   $27.88   $27.90   $27.90  
  Purchase #3 $183.97   10.107%   $202.5638   $202.56   $202.55   $202.60  
  Purchase #4 $163.87   11.687%   $183.0215   $183.02   $183.00   $183.00  
  Purchase #5 $50.45   4.787%   $52.865   $52.87   $52.85   $52.90  
  Purchase #6 $193.68   3.268%   $200.0095   $200.01   $200.00   $200.00  
  Purchase #7 $200.25   8.282%   $216.8347   $216.83   $216.85   $216.80  
  7 purchase totals = $870.29       $942.7943   $942.79   $942.75   $942.80