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 $61.50   12.223%   $69.0171   $69.02   $69.00   $69.00  
  Purchase #2 $33.73   8.850%   $36.7151   $36.72   $36.70   $36.70  
  Purchase #3 $235.37   11.536%   $262.5223   $262.52   $262.50   $262.50  
  Purchase #4 $108.47   12.188%   $121.6903   $121.69   $121.70   $121.70  
  Purchase #5 $96.80   7.791%   $104.3417   $104.34   $104.35   $104.30  
  Purchase #6 $223.82   11.134%   $248.7401   $248.74   $248.75   $248.70  
  Purchase #7 $61.64   4.478%   $64.4002   $64.40   $64.40   $64.40  
  7 purchase totals = $821.33       $907.4268   $907.43   $907.40   $907.30