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 $191.53   6.174%   $203.3551   $203.36   $203.35   $203.40  
  Purchase #2 $18.90   4.800%   $19.8072   $19.81   $19.80   $19.80  
  Purchase #3 $113.85   11.592%   $127.0475   $127.05   $127.05   $127.00  
  Purchase #4 $155.47   6.586%   $165.7093   $165.71   $165.70   $165.70  
  Purchase #5 $142.61   12.568%   $160.5332   $160.53   $160.55   $160.50  
  Purchase #6 $184.35   13.414%   $209.0787   $209.08   $209.10   $209.10  
  Purchase #7 $128.74   5.867%   $136.2932   $136.29   $136.30   $136.30  
  7 purchase totals = $935.45       $1,021.8242   $1,021.83   $1,021.85   $1,021.80