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 $45.47   10.144%   $50.0825   $50.08   $50.10   $50.10  
  Purchase #2 $222.31   9.458%   $243.3361   $243.34   $243.35   $243.30  
  Purchase #3 $207.79   6.437%   $221.1654   $221.17   $221.15   $221.20  
  Purchase #4 $114.98   6.870%   $122.8791   $122.88   $122.90   $122.90  
  Purchase #5 $167.29   8.751%   $181.9295   $181.93   $181.95   $181.90  
  Purchase #6 $146.94   9.486%   $160.8787   $160.88   $160.90   $160.90  
  Purchase #7 $35.83   8.268%   $38.7924   $38.79   $38.80   $38.80  
  7 purchase totals = $940.61       $1,019.0637   $1,019.07   $1,019.15   $1,019.10