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 $241.58   10.372%   $266.6367   $266.64   $266.65   $266.60  
  Purchase #2 $96.51   13.485%   $109.5244   $109.52   $109.50   $109.50  
  Purchase #3 $218.45   6.475%   $232.5946   $232.59   $232.60   $232.60  
  Purchase #4 $235.96   4.736%   $247.1351   $247.14   $247.15   $247.10  
  Purchase #5 $233.89   12.113%   $262.2211   $262.22   $262.20   $262.20  
  Purchase #6 $25.60   11.474%   $28.5373   $28.54   $28.55   $28.50  
  Purchase #7 $53.64   8.776%   $58.3474   $58.35   $58.35   $58.30  
  7 purchase totals = $1,105.63       $1,204.9966   $1,205.00   $1,205.00   $1,204.80