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 $180.85   9.292%   $197.6546   $197.65   $197.65   $197.70  
  Purchase #2 $206.34   7.550%   $221.9187   $221.92   $221.90   $221.90  
  Purchase #3 $134.88   6.634%   $143.8279   $143.83   $143.85   $143.80  
  Purchase #4 $116.59   9.174%   $127.286   $127.29   $127.30   $127.30  
  Purchase #5 $64.51   3.133%   $66.5311   $66.53   $66.55   $66.50  
  Purchase #6 $106.69   6.365%   $113.4808   $113.48   $113.50   $113.50  
  Purchase #7 $149.39   8.184%   $161.6161   $161.62   $161.60   $161.60  
  7 purchase totals = $959.25       $1,032.3152   $1,032.32   $1,032.35   $1,032.30