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 $204.95   5.779%   $216.7941   $216.79   $216.80   $216.80  
  Purchase #2 $62.29   12.270%   $69.933   $69.93   $69.95   $69.90  
  Purchase #3 $56.52   12.170%   $63.3985   $63.40   $63.40   $63.40  
  Purchase #4 $165.79   10.548%   $183.2775   $183.28   $183.30   $183.30  
  Purchase #5 $86.98   8.234%   $94.1419   $94.14   $94.15   $94.10  
  Purchase #6 $216.79   10.435%   $239.412   $239.41   $239.40   $239.40  
  Purchase #7 $173.53   5.865%   $183.7075   $183.71   $183.70   $183.70  
  7 purchase totals = $966.85       $1,050.6645   $1,050.66   $1,050.70   $1,050.60