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 $189.39   6.614%   $201.9163   $201.92   $201.90   $201.90  
  Purchase #2 $186.99   8.169%   $202.2652   $202.27   $202.25   $202.30  
  Purchase #3 $211.88   11.229%   $235.672   $235.67   $235.65   $235.70  
  Purchase #4 $68.95   7.200%   $73.9144   $73.91   $73.90   $73.90  
  Purchase #5 $20.31   4.870%   $21.2991   $21.30   $21.30   $21.30  
  Purchase #6 $170.39   3.410%   $176.2003   $176.20   $176.20   $176.20  
  Purchase #7 $212.86   10.376%   $234.9464   $234.95   $234.95   $234.90  
  7 purchase totals = $1,060.77       $1,146.2137   $1,146.22   $1,146.15   $1,146.20