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 $50.88   4.713%   $53.278   $53.28   $53.30   $53.30  
  Purchase #2 $210.56   6.855%   $224.9939   $224.99   $225.00   $225.00  
  Purchase #3 $59.33   11.274%   $66.0189   $66.02   $66.00   $66.00  
  Purchase #4 $116.44   12.738%   $131.2721   $131.27   $131.25   $131.30  
  Purchase #5 $181.59   10.829%   $201.2544   $201.25   $201.25   $201.30  
  Purchase #6 $241.97   10.547%   $267.4906   $267.49   $267.50   $267.50  
  Purchase #7 $86.88   4.580%   $90.8591   $90.86   $90.85   $90.90  
  7 purchase totals = $947.65       $1,035.1670   $1,035.16   $1,035.15   $1,035.30