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 $219.75   8.315%   $238.0222   $238.02   $238.00   $238.00  
  Purchase #2 $46.86   12.278%   $52.6135   $52.61   $52.60   $52.60  
  Purchase #3 $104.99   4.441%   $109.6526   $109.65   $109.65   $109.70  
  Purchase #4 $125.61   9.385%   $137.3985   $137.40   $137.40   $137.40  
  Purchase #5 $201.32   9.231%   $219.9038   $219.90   $219.90   $219.90  
  Purchase #6 $232.35   13.430%   $263.5546   $263.55   $263.55   $263.60  
  Purchase #7 $24.99   8.249%   $27.0514   $27.05   $27.05   $27.10  
  7 purchase totals = $955.87       $1,048.1966   $1,048.18   $1,048.15   $1,048.30