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 $152.67   12.850%   $172.2881   $172.29   $172.30   $172.30  
  Purchase #2 $213.79   11.535%   $238.4507   $238.45   $238.45   $238.50  
  Purchase #3 $164.54   8.143%   $177.9385   $177.94   $177.95   $177.90  
  Purchase #4 $22.32   7.623%   $24.0215   $24.02   $24.00   $24.00  
  Purchase #5 $232.80   4.836%   $244.0582   $244.06   $244.05   $244.10  
  Purchase #6 $193.25   5.598%   $204.0681   $204.07   $204.05   $204.10  
  Purchase #7 $220.55   6.301%   $234.4469   $234.45   $234.45   $234.40  
  7 purchase totals = $1,199.92       $1,295.2720   $1,295.28   $1,295.25   $1,295.30