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 $51.91   7.848%   $55.9839   $55.98   $56.00   $56.00  
  Purchase #2 $71.61   9.179%   $78.1831   $78.18   $78.20   $78.20  
  Purchase #3 $182.98   12.564%   $205.9696   $205.97   $205.95   $206.00  
  Purchase #4 $206.43   11.337%   $229.833   $229.83   $229.85   $229.80  
  Purchase #5 $153.82   8.582%   $167.0208   $167.02   $167.00   $167.00  
  Purchase #6 $36.35   9.466%   $39.7909   $39.79   $39.80   $39.80  
  Purchase #7 $235.70   5.301%   $248.1945   $248.19   $248.20   $248.20  
  7 purchase totals = $938.80       $1,024.9758   $1,024.96   $1,025.00   $1,025.00