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 $94.29   11.584%   $105.2126   $105.21   $105.20   $105.20  
  Purchase #2 $222.68   8.498%   $241.6033   $241.60   $241.60   $241.60  
  Purchase #3 $9.71   4.354%   $10.1328   $10.13   $10.15   $10.10  
  Purchase #4 $201.32   13.549%   $228.5968   $228.60   $228.60   $228.60  
  Purchase #5 $32.27   11.698%   $36.0449   $36.04   $36.05   $36.00  
  Purchase #6 $232.25   4.120%   $241.8187   $241.82   $241.80   $241.80  
  Purchase #7 $206.52   11.657%   $230.594   $230.59   $230.60   $230.60  
  7 purchase totals = $999.04       $1,094.0031   $1,093.99   $1,094.00   $1,093.90