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 $210.42   13.836%   $239.5337   $239.53   $239.55   $239.50  
  Purchase #2 $230.98   5.505%   $243.6954   $243.70   $243.70   $243.70  
  Purchase #3 $56.28   11.319%   $62.6503   $62.65   $62.65   $62.70  
  Purchase #4 $173.79   11.226%   $193.2997   $193.30   $193.30   $193.30  
  Purchase #5 $113.50   6.619%   $121.0126   $121.01   $121.00   $121.00  
  Purchase #6 $30.66   12.626%   $34.5311   $34.53   $34.55   $34.50  
  Purchase #7 $59.52   11.853%   $66.5749   $66.57   $66.55   $66.60  
  7 purchase totals = $875.15       $961.2977   $961.29   $961.30   $961.30