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 $247.36   6.322%   $262.9981   $263.00   $263.00   $263.00  
  Purchase #2 $123.52   5.739%   $130.6088   $130.61   $130.60   $130.60  
  Purchase #3 $189.43   7.596%   $203.8191   $203.82   $203.80   $203.80  
  Purchase #4 $128.31   4.260%   $133.776   $133.78   $133.80   $133.80  
  Purchase #5 $17.64   12.730%   $19.8856   $19.89   $19.90   $19.90  
  Purchase #6 $186.93   7.445%   $200.8469   $200.85   $200.85   $200.80  
  Purchase #7 $70.37   5.631%   $74.3325   $74.33   $74.35   $74.30  
  7 purchase totals = $963.56       $1,026.2670   $1,026.28   $1,026.30   $1,026.20