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 $183.26   12.362%   $205.9146   $205.91   $205.90   $205.90  
  Purchase #2 $173.70   3.550%   $179.8664   $179.87   $179.85   $179.90  
  Purchase #3 $219.97   3.649%   $227.9967   $228.00   $228.00   $228.00  
  Purchase #4 $159.43   11.385%   $177.5811   $177.58   $177.60   $177.60  
  Purchase #5 $31.39   9.369%   $34.3309   $34.33   $34.35   $34.30  
  Purchase #6 $160.44   7.235%   $172.0478   $172.05   $172.05   $172.00  
  Purchase #7 $5.55   7.416%   $5.9616   $5.96   $5.95   $6.00  
  7 purchase totals = $933.74       $1,003.6991   $1,003.70   $1,003.70   $1,003.70