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 $54.29   8.715%   $59.0214   $59.02   $59.00   $59.00  
  Purchase #2 $173.32   7.689%   $186.6466   $186.65   $186.65   $186.60  
  Purchase #3 $215.60   5.823%   $228.1544   $228.15   $228.15   $228.20  
  Purchase #4 $133.45   6.848%   $142.5887   $142.59   $142.60   $142.60  
  Purchase #5 $106.31   8.260%   $115.0912   $115.09   $115.10   $115.10  
  Purchase #6 $203.85   8.546%   $221.271   $221.27   $221.25   $221.30  
  Purchase #7 $20.66   13.367%   $23.4216   $23.42   $23.40   $23.40  
  7 purchase totals = $907.48       $976.1949   $976.19   $976.15   $976.20