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 $243.86   6.623%   $260.0108   $260.01   $260.00   $260.00  
  Purchase #2 $223.55   8.127%   $241.7179   $241.72   $241.70   $241.70  
  Purchase #3 $120.58   12.133%   $135.21   $135.21   $135.20   $135.20  
  Purchase #4 $106.51   13.810%   $121.219   $121.22   $121.20   $121.20  
  Purchase #5 $22.31   9.683%   $24.4703   $24.47   $24.45   $24.50  
  Purchase #6 $208.62   13.502%   $236.7879   $236.79   $236.80   $236.80  
  Purchase #7 $57.49   13.310%   $65.1419   $65.14   $65.15   $65.10  
  7 purchase totals = $982.92       $1,084.5578   $1,084.56   $1,084.50   $1,084.50