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 $173.30   13.671%   $196.9918   $196.99   $197.00   $197.00  
  Purchase #2 $243.52   6.618%   $259.6362   $259.64   $259.65   $259.60  
  Purchase #3 $95.75   9.235%   $104.5925   $104.59   $104.60   $104.60  
  Purchase #4 $174.54   10.729%   $193.2664   $193.27   $193.25   $193.30  
  Purchase #5 $206.26   10.227%   $227.3542   $227.35   $227.35   $227.40  
  Purchase #6 $195.35   8.415%   $211.7887   $211.79   $211.80   $211.80  
  Purchase #7 $60.77   9.534%   $66.5638   $66.56   $66.55   $66.60  
  7 purchase totals = $1,149.49       $1,260.1936   $1,260.19   $1,260.20   $1,260.30