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 $33.86   8.183%   $36.6308   $36.63   $36.65   $36.60  
  Purchase #2 $115.92   6.638%   $123.6148   $123.61   $123.60   $123.60  
  Purchase #3 $187.94   5.452%   $198.1865   $198.19   $198.20   $198.20  
  Purchase #4 $163.75   3.352%   $169.2389   $169.24   $169.25   $169.20  
  Purchase #5 $246.81   3.230%   $254.782   $254.78   $254.80   $254.80  
  Purchase #6 $89.58   10.517%   $99.0011   $99.00   $99.00   $99.00  
  Purchase #7 $136.55   12.320%   $153.373   $153.37   $153.35   $153.40  
  7 purchase totals = $974.41       $1,034.8271   $1,034.82   $1,034.85   $1,034.80