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 $9.27   5.217%   $9.7536   $9.75   $9.75   $9.80  
  Purchase #2 $223.68   3.557%   $231.6363   $231.64   $231.65   $231.60  
  Purchase #3 $56.40   13.108%   $63.7929   $63.79   $63.80   $63.80  
  Purchase #4 $181.29   8.846%   $197.3269   $197.33   $197.35   $197.30  
  Purchase #5 $241.75   13.557%   $274.524   $274.52   $274.50   $274.50  
  Purchase #6 $162.95   5.501%   $171.9139   $171.91   $171.90   $171.90  
  Purchase #7 $119.68   6.542%   $127.5095   $127.51   $127.50   $127.50  
  7 purchase totals = $995.02       $1,076.4571   $1,076.45   $1,076.45   $1,076.40