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 $174.53   12.840%   $196.9397   $196.94   $196.95   $196.90  
  Purchase #2 $177.42   13.541%   $201.4444   $201.44   $201.45   $201.40  
  Purchase #3 $8.52   9.241%   $9.3073   $9.31   $9.30   $9.30  
  Purchase #4 $228.78   11.701%   $255.5495   $255.55   $255.55   $255.50  
  Purchase #5 $12.28   11.619%   $13.7068   $13.71   $13.70   $13.70  
  Purchase #6 $33.67   6.738%   $35.9387   $35.94   $35.95   $35.90  
  Purchase #7 $155.29   11.269%   $172.7896   $172.79   $172.80   $172.80  
  7 purchase totals = $790.49       $885.6760   $885.68   $885.70   $885.50