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 $225.87   11.582%   $252.0303   $252.03   $252.05   $252.00  
  Purchase #2 $34.45   6.200%   $36.5859   $36.59   $36.60   $36.60  
  Purchase #3 $210.36   6.649%   $224.3468   $224.35   $224.35   $224.30  
  Purchase #4 $52.89   3.708%   $54.8512   $54.85   $54.85   $54.90  
  Purchase #5 $181.67   10.296%   $200.3747   $200.37   $200.35   $200.40  
  Purchase #6 $194.85   9.617%   $213.5887   $213.59   $213.60   $213.60  
  Purchase #7 $17.68   4.768%   $18.523   $18.52   $18.50   $18.50  
  7 purchase totals = $917.77       $1,000.3006   $1,000.30   $1,000.30   $1,000.30