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 $202.83   12.527%   $228.2385   $228.24   $228.25   $228.20  
  Purchase #2 $84.47   13.637%   $95.9892   $95.99   $96.00   $96.00  
  Purchase #3 $76.72   6.197%   $81.4743   $81.47   $81.45   $81.50  
  Purchase #4 $180.33   11.607%   $201.2609   $201.26   $201.25   $201.30  
  Purchase #5 $230.35   11.136%   $256.0018   $256.00   $256.00   $256.00  
  Purchase #6 $240.72   7.794%   $259.4817   $259.48   $259.50   $259.50  
  Purchase #7 $233.55   4.271%   $243.5249   $243.52   $243.50   $243.50  
  7 purchase totals = $1,248.97       $1,365.9713   $1,365.96   $1,365.95   $1,366.00