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 $55.77   7.754%   $60.0944   $60.09   $60.10   $60.10  
  Purchase #2 $166.96   8.648%   $181.3987   $181.40   $181.40   $181.40  
  Purchase #3 $63.79   8.251%   $69.0533   $69.05   $69.05   $69.10  
  Purchase #4 $166.77   10.563%   $184.3859   $184.39   $184.40   $184.40  
  Purchase #5 $165.52   6.603%   $176.4493   $176.45   $176.45   $176.40  
  Purchase #6 $219.86   13.739%   $250.0666   $250.07   $250.05   $250.10  
  Purchase #7 $123.97   5.708%   $131.0462   $131.05   $131.05   $131.00  
  7 purchase totals = $962.64       $1,052.4944   $1,052.50   $1,052.50   $1,052.50