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 $211.45   11.232%   $235.2001   $235.20   $235.20   $235.20  
  Purchase #2 $36.33   13.641%   $41.2858   $41.29   $41.30   $41.30  
  Purchase #3 $161.39   9.172%   $176.1927   $176.19   $176.20   $176.20  
  Purchase #4 $48.78   5.636%   $51.5292   $51.53   $51.55   $51.50  
  Purchase #5 $27.54   11.155%   $30.6121   $30.61   $30.60   $30.60  
  Purchase #6 $170.77   4.700%   $178.7962   $178.80   $178.80   $178.80  
  Purchase #7 $197.71   6.712%   $210.9803   $210.98   $211.00   $211.00  
  7 purchase totals = $853.97       $924.5964   $924.60   $924.65   $924.60