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 $82.54   12.232%   $92.6363   $92.64   $92.65   $92.60  
  Purchase #2 $94.58   8.448%   $102.5701   $102.57   $102.55   $102.60  
  Purchase #3 $157.29   7.467%   $169.0348   $169.03   $169.05   $169.00  
  Purchase #4 $117.63   11.704%   $131.3974   $131.40   $131.40   $131.40  
  Purchase #5 $239.51   6.401%   $254.841   $254.84   $254.85   $254.80  
  Purchase #6 $62.35   7.449%   $66.9945   $66.99   $67.00   $67.00  
  Purchase #7 $72.96   6.374%   $77.6105   $77.61   $77.60   $77.60  
  7 purchase totals = $826.86       $895.0846   $895.08   $895.10   $895.00