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 $48.42   10.369%   $53.4407   $53.44   $53.45   $53.40  
  Purchase #2 $237.80   6.112%   $252.3343   $252.33   $252.35   $252.30  
  Purchase #3 $167.49   5.674%   $176.9934   $176.99   $177.00   $177.00  
  Purchase #4 $63.86   10.506%   $70.5691   $70.57   $70.55   $70.60  
  Purchase #5 $202.89   12.442%   $228.1336   $228.13   $228.15   $228.10  
  Purchase #6 $128.98   12.619%   $145.256   $145.26   $145.25   $145.30  
  Purchase #7 $10.80   10.529%   $11.9371   $11.94   $11.95   $11.90  
  7 purchase totals = $860.24       $938.6642   $938.66   $938.70   $938.60