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 $54.32   10.373%   $59.9546   $59.95   $59.95   $60.00  
  Purchase #2 $184.56   12.338%   $207.331   $207.33   $207.35   $207.30  
  Purchase #3 $229.74   7.777%   $247.6069   $247.61   $247.60   $247.60  
  Purchase #4 $247.86   7.282%   $265.9092   $265.91   $265.90   $265.90  
  Purchase #5 $189.41   7.154%   $202.9604   $202.96   $202.95   $203.00  
  Purchase #6 $134.70   8.140%   $145.6646   $145.66   $145.65   $145.70  
  Purchase #7 $123.36   6.191%   $130.9972   $131.00   $131.00   $131.00  
  7 purchase totals = $1,163.95       $1,260.4239   $1,260.42   $1,260.40   $1,260.50