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 $165.88   12.553%   $186.7029   $186.70   $186.70   $186.70  
  Purchase #2 $99.99   10.571%   $110.5599   $110.56   $110.55   $110.60  
  Purchase #3 $152.35   3.646%   $157.9047   $157.90   $157.90   $157.90  
  Purchase #4 $238.30   10.374%   $263.0212   $263.02   $263.00   $263.00  
  Purchase #5 $7.51   5.825%   $7.9475   $7.95   $7.95   $7.90  
  Purchase #6 $105.62   3.440%   $109.2533   $109.25   $109.25   $109.30  
  Purchase #7 $173.47   10.184%   $191.1362   $191.14   $191.15   $191.10  
  7 purchase totals = $943.12       $1,026.5257   $1,026.52   $1,026.50   $1,026.50